I was issued a NIB Model 15 (no distinct department markings) when I returned from the academy in August 1978 as a Police Patrol Officer with the Lake Forest Illinois Police Department.
Although we were sworn officers (I was sworn in on June 13, 1978) and were legally authorized to carry firearms, the department policy was to not allow on-duty carry until after completion of the academy AND successfully passing the department's firearms qualification. One of my classmates at the academy passed everything the academy required, but it took him two weeks to pass the department's qualification. I remember he had a blister on his right index finger from all of the shooting and dry-firing he had to do to pass.
You had to carry the Model 15 until you passed probation (one year from date of hire), then you could carry any revolver approved by the department's armorer, as long as it would chamber the department issued ammo (W-W .38 Special +P 158 grain LHP-the "Chicago load"), and had a four inch barrel. The hot gun on the street at the time was the S&W Model 66, but you couldn't find them, at least at a price a rookie cop could afford, so my first personally owned duty gun was a stainless Ruger Security Six. Later, I carried a Colt Python that my wife bought me as a combination first wedding anniversary/birthday present (I still have that gun and wife!).
I was also a Security Specialist (Sky Cop) in the Air National Guard and while we mostly carried M-16s for weapon system security, supervisors and security controllers also carried Model 15s. I was fortunate enough to be selected for Undergraduate Navigator Training and when I came back, I had to again qualify on the Model 15 as a combat-ready aircrew. The last time I carried a Model 15 was when I deployed to Saudi Arabia in 1990 during Operation Desert Shield. As soon as I turned it into the armory, I was immediately issued a M-9, for which I had no holster. Our Life Support guys spent a lot of long hours sewing new holsters that would fit the M-9 onto our survival vests.