1932-34 "DR" registration prefix numbers?

[SoCal32]

I've got a '32 and a '34 with titles from the 50s that both VINs start with DR (instead of B or 18). Both cars are most likely from California and are completely unrelated as to sellers and have been in the family for decades. I know back in the day the DMV and dealers were a little more laxed when it came to paperwork. Just curious that 2 of our cars had this same thing. Wasn't sure if this was a number that was stencilled on the firewall or an engine number. Anyone have any ideas?