It's not stealing if it is abandoned. The definition of abandoned is not clear, but in this case they abandoned it. You have no right to chain your crap to a post in a public area of a city and expect people to respect your property right to it forever.
2000 Montague CX, I do not recommend it, but still ride it.
Strida 3, I recommend it for rides < 10mi wo steep hills.
2006 Rowbike 720 Sport, I recommend it as an exercise bike.
1996 Birdy, Recommend.
Wieleder CARiBIKE (folding), decent frame.