It's pimp my pistol time. In the last decade military and police assault rifles have been heavily accessorized with rail mounted scopes, lights, and laser aiming pointers (to name the most popular ones, there are many more). In the last few years such rail mounted accessories have become increasingly popular with pistols (often not the one you carry in a holster).
There are now lightweight (aluminum) rail adaptors for pistols. With these you can add popular items like lights and laser aiming pointers. Another popular accessory is a glass breaker (to get through glass without injuring yourself or taking your aim away from a suspect). For those who like to try everything there are also adaptors that will give your pistol a stock and front hand grip, plus lots of rails for your favorite accessories. The resulting weapon looks like a machine-pistol without the long box magazine (and firing semi-auto from 17 round clips).
For most pistol users, a light or laser aiming device that can be quickly clipped onto a pistol does the job. But for the truly ambitious, or obsessed, only rails will do.