Engine # significance

Can somebody explain the significance of the nimber stamping ... Thanks

No nimber stampings on my bikes but the stamps look real enough. :|

Hahaha Yes the "nimber" looks original and on MK3 4/75.......

I don't know what it is supposed to signify, but "H 20" or "H 22" is often found stamped on Mk3 cases in that position.
My non-original Mk3 crankcase is stamped H 22.

Edit: Thinking about it, there is also the possibility that the "H" number may have been a marking on the crankcase casting pattern?