On my way out for a ride, I encountered this in front of a neighbor’s house:
That both tires were flat and the chain was rusted and “pretzeled” were signs of what I suspected.
Two other things clued me in.
Not only was the serial number, except for the first digit, removed; so was another unique (for Citibikes and other share bikes):
The mechanism that locks the bike into the dock was removed. Here is what the front of a normal Citibike looks like:
I called Citibike and brought the pilfered (and probably joy-ridden) bike to the port down the street from my apartment.
