This site has a long log posted by someone and indicates the mark "Carl Busse, Mainz" is found on WWII Nazi German Hi-Power (rifle) holsters.

This collector claims ownership of a "German M38 (one piece) Gladiator helmet", same makers mark, states is bore a swastika but was rubbed off.

This site sold a gun, German Luger BYF, 1942 with Holster, and states the following about the holster: "Included is a P08 marked holster showing a Waffenamt 927 mark coded JKH 42. JKH was the code for Carl Busse Fabrik Fur Heeresausrustungen Aus Stoff und Leder, Mainz, Kurfurstenstrasse. Waffenamt Inspection numbers 286,927 and 179 were assigned to Carl Busse. Originally a brown holster dyed black and now much scuffed. A WWII vet bring back piece. "

A site selling a knife with same manufacturer stamp on the sheath as your piece carries. This one also has a swastika on it.

A UK militaria shop, listing at bottom of page, "Pony Fur Backpack Good strong hairs to cover.Patina to hard ware.Traces of wartime grey paint remaining.Type with d-rings for attaching directly to the y-straps.Mice have been happily grazing to cloth interior.Maker marked and dated JKH 41-Carl Busse Mainz.Still good for display.In Good condition." $27.20 US Dollars.

What wikipedia says about Mainz, Germany. "During World War II the citadel at Mainz hosted the Oflag XII-B prisoner of war camp...During World War II, more than 30 air raids destroyed about 80 percent of Mainz city centre, including most of the historic buildings. Mainz fell to XII Corps, 90th Division, of the Third Army under the command of General George S. Patton, Jr. on 22 March 1945...From 1945 to 1949, the city was part of the French zone of occupation.

Probably most informative so far, this PDF article talks about how German WWII military artifacts, especially weapons, were inspected and the die stamps put on by inspectors. "Collectors and other observers of WWII German military artifacts, especially weapons, often see small die stamps on them with a stick figure representation of the German Reich eagle and a number. Commonly referred to as "Waffenamts", they were inspection stamps which identified the item as being inspected and passed, at some stage of its manufacturing
process for the German Army.". (This might be the guy to email, he includes his address, bottom of page 5.) Your mark shows up on pps 21, 27 and 39 of the document linked to above.

Based on codes and abbreviations listed, here's what I came up with on items bearing the mark Carl Busse, Mainz:
WaA [Waffenamt] code was a commission number assigned to the officer in command of an inspection team at the various factories.
*Carl Busse has 2 WaA codes, #286 and #927 in this article.
*The code assigned to Carl Busse factory: jkh. (As noted in 3rd link above as well.)
*Items inspected include a flaregun holster; horse leather equipment; FN HP Holster (don't know what FN HP stands for, but HP could be 'high power' as in rifle); PO8 Holster
*Factory name: Carl Busse
*Place (location): Mainz(RP) RP stands for Rheinland-Pfalz
*Years listed: 1937, '39, '41, '43, and 1941-42

So, what that would indicate is the scabbard (sheath for swords or other large blades) shown in your photo was made at the Carl Busse Factory, Mainz, Rheinland-Pfalz, German, 1940. Since most items found so far are of a leather nature perhaps those type items were most frequently manufactured at the Busse factory?

As far as the sword, sometimes what is doesn't look like helps rule out possibilities. Here's a diagram identifying sword parts and terminology. this site shows the lion head was used on German swords in WW1 & II, but the head is different than yours (and many eyes are rubies). Another site,auction of a WWII German Officer's dress sword, lion head, ruby eyes (again different than yours), asking price $1295.00

What I'm finding puzzling is the grip appears to be bone, where most WWII German military swords I've hit upon so far have metal handles. (Bone was/is commonly used in hunting knives, but that's a whoppin' long blade to have been used for hunting! Unless it was really large game.)

Ooohh, wait a minute! I just found a much older German hunting dagger, circa 1860-1880, lion's head similar to yours, hooves on the cross guard, bone (stag) grip. Even has the clamshell guard.

Another similar one! Called a "Forestry Dagger" here (3/4 of the way down the page). Grip is different, but many other similarities. "This is the lion-head hunting sidearm as used by forest masters in the service of the Kaisers and kings. The lion-head version was the type used by the Bavarian service. The length is 21 inches overall and the blade is 15 inches."

That's as close as I got, now hitting dead ends. I'm going to take a stab (no pun intended) that it's a long hunting/forest type dagger, perhaps not specifically meant for warfare but possibly used in that regard? Does the leather scabbard fit perfectly, as if designed for the blade? If so, that would be a good indicator that the scabbard is the intended mate to the sword/dagger, so it's also German, circa WWII. If it's not quite a perfect fit, perhaps it was an older German hunting dagger that was paired with the WWII scabbard. Perhaps brought back home by a soldier, as was often done?

Now if I could just unearth that same kind of info on the half dozen or so mystery pieces in my possession I'd be a pretty happy camper! ;D

calliope brings up something I noticed in my searching. Many blades mentioned did have markings, but many also were partially or nearly completely worn off (age?use?). But I'm hoping the OP sees this again and can inspect that blade very closely to see if there is evidence of some kind of marking on it.

I noticed something when I was looking at pictures of it. The eyes appear to be different:

I'm not sure if that means anything.

I'm going to look at the blade tomorrow and see if there are any markings on it.

More intriguing. I zoomed in really close and is it just me or does it look like there are recesses where a stone once sat for each eye? (most pronounced in the second photo, face facing left) Rubies like some of the other swords linked to above? Fascinating detail in the carving all around!

The one from "much older German hunting dagger" link above is closest in appearance so far. Here's what the seller says about it: "German Hunting dagger with lions head pommel. Circa 1860-1880. 14" blade and 20" overall. Stag handle scabbard is very good with some surface age cracking but very solid. This one looks like it was actually used as most were for appearance. $995.00"

If the above description is correct, and based on appearances of other WWII daggers & swords seen, I'm wondering if the one you have is not older than WWII era, or at very least not married to the scabbard it's in. Because a little detail that's been bugging me is the way yours sits in the scabbard compared to the one found so far closest in appearance. If you look at the old German Hunting dagger, the sheath only goes up to the clamshell guard.

But yours, when in the scabbard, the lion's head rises above what appears to be a belt loop? Just a tad, but it's still above it. If it is indeed a hunting dagger, as the handle would lead one to think, picture someone wearing it out in the woods, attached to their belt. Thinking of all my hikes and hunts in the woods back home on the farm, climbing around rocky stream beds, up almost vertical terrain, wooded hills, maneuvering around thick brush and trees branches, it doesn't take much for something worn on the body to get caught on something or bumped and poke into the wearer. So the closer and snugger to the body the better. So if someone were carrying your dagger on a belt, hiking, mounting or dismounting a horse, would that not be slightly awkward, making the lion's head a bit...floppy? Just enough to be inefficient and annoying to the wearer? Almost (but not quite) poke into the wearer's body, especially when bent at the waist? Or that little bit of lion head sticking above could be just enough to catch a branch, or tangle in a thicket of briars. As is, would it force the wearer to stop every few yards due to a tangle? Or place a hand on the lion's head to hold it snug to the body when bending or walking in dense woods? Would it not be more functional/comfortable for the wearer to have the lion's head sit lower and therefore more snugly in the scabbard, versus protruding that little bit beyond the top of the leather scabbard loop? I could be going way too far into left field on that one, but it just makes me pause just a bit and wonder if your dagger and scabbard are actually not a married pair.

Here are comparison photos:
Old hunting dagger:

Yours:

Older hunting dagger

Yours

Yours has a collar at the base of the lion's head, where the other has nothing. I can't tell from your photos, looks like something is engraved on the band between the hooves, above the clamshell? Is it oak leaves and acorns like the comparable one?

OK, daydreaming now!

http://www.lakesidetrader.com/Hunting and Forestry.html

http://germandressdaggers.com/hunting association.htm

These "daggers" were sometimes semi-ceremonial, and often fancy presentation pieces (gilt, engraved, ivory handled, etc.). You need to research the "German National Hunting Association" (Reichsforstdienst) It was established well before the Nazi party.

Maybe there was a set of rules for what rank of forester got what materials: carriers of wood and antler swords ranking below ivory and sterling swords? The wood and antler would be more practical if it was meant to be used.

Don't give the scabbard too much importance in dating the knife - they wear out or get damaged, and a good knife may have been in several sheaths.

Closest match:
http://www.militaryrelics.com/photos/story.cfm?id=5268 Look down the page for the Bavarian Jager hirschfanger