Here’s an example of what I’m talking about. This anonymous fellow was captured by a bank security camera and the photo is marked PC 45080. Often in these cases, the PC number will be rendered PC 450 (80), in which the last two numbers apparently signify the year. The matter is further complicated because some of the bank robbery photos have FBI numbers (which begin 91-123456) and others have LAPD DR numbers.
(And yes, there are lots of men with hairy chests in these pictures. It was the era.)
By the way, the LAPD apparently changed its numbering system to this protocol about 1983: The first two numbers are the year. The next two are the LAPD area. The rest are the sequential numbers issued through the year. So 83 01-23456 would be an incident that occurred in 1983 (83) in LAPD’s Central Area (01) and given the number 23456
Here’s another example:
Here’s DR 76 468-163, a drawing by F. Ponce (I have dozens of sketches by Ponce, by the way), of two women, which also has a PC number PC 144 (76). There is no crime listed as 144 in the California Penal Code, so it seems more likely that this is some sort of cataloging system.