I was curious, without trying to start and run a K&B .65 Sportster engine, how can you tell if it is a Government Drone special or not?

I have seen some engines without a number on the left mounting lug and some engines with a number stamped into the left mounting lug.
But some numbers start with a J, some with a G and I think that there were some start with a R on them too. But more than one engine may have the same number on it too. So it apparently is not a serial number then. For example G29065.