I haven’t seen that either, but the font is very consistent with similar ones I’ve seen on Parabellum / Swiss Lugers.
The P59 was not stamped at the factory but at the army arsenal. Still very original since it belonged to the army.
It’s a very desirable pistol imo, only the 1512th produced for the Swiss army, first batch delivered in 1949. They were originally built without the halfcock, however many had it added by Sig for safety reasons but not all of them. The ones without it are rarer and more sought after
I have the 1811th, it only has a P on the trigger guard without the year.
Check or ask the seller to check that the barrel and hammer group are serialised to the gun
Also the original mags were high polished with a horizontal cross sanding on the bottom
I have a theory as to the P 59 : it is very unusual for an army pistol to be released and privatised after only 10 years. Maybe it was a high ranked officer who asked to keep it after his service and retirement. In any case they were still stamping the P and the year (two digits) on Parabellums (Luger) a practice they gave up eventually, stamping only a P or nothing at all.