Bike theft has been a problem just as long as there have been bicycles. College campuses routinely warn students about theft and just as routinely, bikes are stolen from campus in ever increasing numbers. When I was in college in the late 80s, the campus police used a battered white bike as bait, leaving it unlocked next to different college buildings and waiting for it to be stolen. School lore reported that it usually took less than thirty minutes. That was more than twenty years ago and I'm pretty sure that the timing hasn't changed much. One writer spent several months in several cities setting up his bike for theft and chronicling the fascinating results. In America's underworld, he reports, there are four major currencies: cash, drugs, sex and bikes.
As biking has become more and more popular over the last decade, bike security has become big business. There are three main types of bike lock: U-locks, the familiar U-shaped metal locks, often manufactured by Kryptonite; cables, which are simple to use but easily circumvented and chains with padlocks, which are efficient but heavy and time consuming to lock and unlock. The Santa Barbara Independent goes over the different types of locks but ruefully admits that if you must leave your ride on the street, you're better off with a cheap bike. Wired magazine also recently reviewed a variety of different bike locks, rating them for ease of use, difficulty of theft and weight, which is always a consideration when it comes to bike locks. Most high end locks offer a theft guarantee, so make sure to complete the required paperwork before you use your lock.
The Insurance Information Institute has a checklist for keeping your bike safe. They suggest marking your bike, writing the serial number down and taking several photos of it to help police in identification. They also recommend registering your bike with local police and the National Bike Registry. Bicycle theft is covered by your homeowners or renters insurance but there is ordinarily a rather high deductible. If your bike is particularly valuable, you may want to speak with your independent insurance agent about a floater policy to keep it covered at all times.