A 1980's magazine article that I saved says P6 for Hamburg.
The "crosshair" B symbol is a 1980's mark.
Everything in the Bucheimer saga mid to late 80's got really mixed up.
I'll put down 81 tentatively as a designation for Sig!!
Thanks for the useful info, P6 is actually the police version of the P225, only slightly modified. Unfortunately further information is (as far as i know) available in German only:
SIG Sauer P225 – Wikipedia
the holster actually fits a few models of the 220- line of Sig Sauer.