I may pick up the pipe if I found it attractive, but I'd clean it very, very, well eg soak in iso for a week, scrub, standard 2x2x2 water/bleach/water, then out into the sun for UV to finish off. Even then I probably wouldn't be able to use it, call it nurse's paranoia.

It might just be grotty smoking remains or something nastier left as a prank on anyone stupid enough to smoke it. I worked with a guy in a city forensic psych unit who did that sort of thing for kicks. I'm sure there are more who haven't been locked up as 'criminally insane', thus I am wary of things I find in parks, bus shelters and public phone boxes.