We are having fun in the G+ Boing Boing community. Our friend Rob Walker posted this photo and said:
I was in San Francisco recently and walking from Market/8th to the SF CalTrain station I kept noticing these odd little things, mounted about 10 feet off street level, a few-inches-wide tire-like object often (but not always) accompanied by small target symbols. What is it, is it functional, or some sort of street art thing. Anybody know?
Mark Frauenfelder is the founder of Boing Boing and the editor-in-chief of MAKE and Cool Tools. Twitter: @frauenfelder. His new book is Maker Dad: Lunch Box Guitars, Antigravity Jars, and 22 Other Incredibly Cool Father-Daughter DIY Projects