Very interesting! That's a new one on me. I've seen HW 35's made in '66 and '67; HW 50's from '58 and '67; and HW 55's from '63, '65, and 67. None of them had the "Prazision" mark.
I sent this photo and question to the biggest vintage airgun expert I know: Danny Garvin, creator of the fabulous "Vintage Airguns Gallery" web site. His reply:
I haven't seen that before either. I can only speculate it was a short-lived, quickly-abandoned, scheme to incorporate 'precision' formally into the Weihrauch name?
If he hasn't seen it...you may have something pretty rare! It's striking that the marking is so much larger than the usual one. In those days HW's did not use breech shims, and the second line is so long that the "35" has been partly obscured by wear from the breech jaw.