Says PL (= linear Polarizer), on the filter, Rukshan.
RE: linear vs. Circular: There is surprisinly little difference. The only reason why companies introduced circular polarizers (CP) was to avoid light extinction on the exposure sensors of many modern AF SLRs. So they just added a quarter plate filter to the back of the linear polarizer and called it CP, or PC. Contrary to common misconceptions, there is no negative effect whatsoever in the images using linear filters, bearing in mind however that some exposure compensation may (or may not) be needed.