I found the answer.

Instructions:
Lay the socks flat on your work surface so that the bottom side is up. Now, simply use the puffy fabric paint to make dots, lines, or other shapes on the bottom of the sock. This will transform the ordinary socks into socks with a non-skid bottom.

Depending on how thick the paint is applied, the designs may take several hours to dry! Once the bottoms are dry, you can decorate the top of the sock if you want. Wear and enjoy.

or check out video below

Here is a link that might be useful: non-slip socks

I found puffy paint to wear off rather easy, here is what we do for our felted slippers, and they become non-slip PLUS waterproof on the bottom:

We wrap ours (the parts we dont' want sprayed)in cheap plastic bag, then spray then with plasti-dip (we buy the spray rather than the paint on kind, works better)..lightly a few times. This works great for a few reason's. Lightly spraying leaves a texture on the bottom, aiding in slip-proof, and the plasti-dip is rubber, also making non-slip.

We get the plasti-dip at Home Depot. I've only gotten it in black, but I figure it's on the bottom of a slipper, so who cares. They do sell other colors I guess, just on-line. Ace Hardware is suppose to carry also. One can does about 3-4 pairs of slippers depending on how many layers you put on, and how big the slippers are. DO IN WELL VENTILATED AREA!!

Vickey-MN

oh. my. gosh.

I've been looking for a pair of those slipper socks with the nonskid stripes or dots on the bottom. Couldn't find em without a too big pricetag. I want them, not for slippers, but to make a non skid camera holder for the front of the car! OMG! PUFFY PAINT! DUHHHHHHHH!!!! I'd never heard of plasti dip. I'll have to check that out too.

I wore non slip slippers on stairs one time and never again. I was going down the stairs the non slip worked but the top was so stretchy which made me go head first. I caught myself just in time to keep from breaking my neck. Around the house they may be fine, but for me I want something more solid to wear or just go barefoot which I can't do anymore.