Welcome to HandGunForum.net!
I have a S&W model 15 that I use regularly; I bought it because I carried one while in the USAF, and I really enjoy shooting this size and style of revolver. Mine is a 4" barrel version, but otherwise, it is probably almost identical to the one you are looking at. The S&W model 15 is a .38 Special caliber, 6-shot, swing-out cylinder, medium-frame (K-frame), blue-steel revolver, that can be fired in two different modes; single-action (thumb-cocking the hammer and lightly squeezing the trigger for each shot) or double-action (squeezing the trigger through a long, heavy pull that cocks and then releases the hammer for each shot). It has a fully-adjustable rear sight, with slotted adjustment screws for windage (left and right adjustment) and elevation (up and down). The front sight is usually a serrated steel ramp-style fixed blade. Normal factory-issued grips were made of checkered walnut, and were the smaller service-style grips. Used model 15s are often seen with aftermarket (non-factory) rubber grips, which are usually rather ugly, although they can be very functional in giving the shooter a secure grasp on the handgun.
These are great revolvers, and one in excellent condition might bring $400 or more. Used police department trade-in guns with worn external finishes are worth less, but still can be fine shooters.