In the 1960's and 1970's, the Combat Magnum/Model 19 was probably the most popular optional sidearm carried by U.S. cops. Lots of them were purchased by the officers with their own funds and many departments bought and issued them, too. It remained so until some of the luster was stolen by the Model 66, the same gun made in stainless steel. They were often hard to find and many dealers marked them up well over suggested retail. The popularity of both waned when the switch to semiautomatic pistols gathered steam.

I think that when shooters mentally picture the S&W revolver, the image of the 4 inch Combat Magnum most often comes to mind.

They are such a useful gun, that when an owner decides to sell his, it often goes to a shooting buddy, with no advertising involved.