PL prefix is for P5 LTD (1973 to 1976).
PM = P6 LTD
PN = FC LTD
So, you have P5/P6 C Pillar badges. eBay seller Betterthannos has been reproducing these for a while now and given the option, I would be buying these ones, as compared to the NOS ones. However, being NOS, they will certainly have some value.