Get some Brasso (or similar brass/copper polish. Apply to a small section of pipe with a piece of cloth; rub for a few minutes. If it's copper, you'll know it.

I'm going to try this -- thanks. If the pipe is painted (I can't tell... lots of dirt and stuff...) is it OK to sand a copper pipe?

scratch it with a butter knife. rub it with a brillo. try the brasso. If it is copper you can sand it. You could polish it up like a stripper pole if you wanted to, but if the brown color you describe is just the deep brown color of the oxidized copper surface, remember that it took 80 years to get that way and you may find yourself wishing you'd have left it alone. I'd try just cleaning it first and then ponder if I wanted it polished shiny.

try a Scotch-Brite® Heavy Duty Scour Pad # 223 ( green in color) which can usually be found at lowes.
these pads are very aggressive. I use these pads for cleaning copper before soldering