I have an Italian SXS I bought in Italy which has a 199 serial number. Interesting but of no value I guess.
I also have a 4 digit serial number Ruger Red Eagle my buddy gave me before he died. Checking with the factory I learned it was an early model and likely built in Ruger's garage when they first started making them. It seems in those years they skipped a bunch of numbers so it was in effect a low number gun with a higher serial number.
I traded off a 629 with a member here that had a serial number like BRU6100 or something similar. It made no difference in the trade but the fact it was NIB with papers meant something.