Colt Detective Special 2" barrel .38 Special, six shots.
Colt Police Positive 4" barrel, .38 Special six shots.
S&W Military & Police, started production in 1899, still making them (the model 10). The common cop gun everywhere for nearly fifty years at least. Six shot .38 Special.
Colt M1917 New Service .45 ACP with moon clips holding six shots.
S&W M1917 Triple Lock .45 ACP with same (both were substitute issue in WW1 and WW2)
Either of those in their .45 Colt models, also very common at the time.
In automatics, the M1911A1 .45 ACP Colt service pistol, the .32 ACP or .380 ACP Colt Model M (M1903 or M1908), common pocket pistols of the time along with the Detective Special.