[mass A man]

I doubt the "P" was for the make of the car it was on. Some aftermarket caps came with a stack of letter badges and the little drive nails. The owner would pick which letter he wanted (usually had to do with his name) and nail it to front of the rad. cap. Years ago I sold a stack of those letter badges with an aging pot metal cap in the box, from the '20's. Got a whopping $5. for it.