Prior to adopting the Beretta M92, SFPD permitted all types of S&W revolvers. Back in the '60s, they even allowed the .41 Magnum to be carried on duty. Today they're carrying a Sig-Sauer in 40 S&W.
The San Francisco Sheriff's Department allowed all types of revolvers, but issued the Model 15 or Model 67. Today they're issuing Glocks.
NYPD carried Colt Police Positive.
I think LAPD carried S&W Model 19 revolvers. The single action notch on the hammer was ground off to prevent the gun being used in the single action mode.