The Chicago bicycling community is up in arms about a possible white van that is stealing bikes in the Loop. Craigslist's bikes section has a lot of the details. In the meantime, if you ride on two wheels, remember to use two U-Locks, not a cable lock, and if you can, register your bike with the Chicago Police. Mr. Bike also recommends putting your name and address in the seat-post tube since some unsophisticated thieves might not look there. Also, add stickers, duct tape, and other markings to make it distinctive and thus less attractive to thieves.