Well Switzerland had and has a militia army, soldiers did serve till the year they reached the age of 48 and Officers even served longer (nowadays it's all less long).
As all Swiss armed militia members the Officers and NCO's armed with pistols got the opportunity to keep or turn in their guns at the end of their military career, when they decided to keep the gun it was "de-militarized" by the arsenal by stamping it as P(rivate) and till 1964 the year of privatization was added also.
Just a P means privatized past 1964.
Guisan.
Guisan.