This looks to be a traditional duplex-type cancel on this common stamp. I just have not been able to identify what "PTS" may have stood for in the killer portion of the cancel.

I've seen similar cancels with "RMS" (Railway Mail Service), etc., but not "PTS". Any ideas?
(It also proves a point of what has been said in other threads here about how much postal history is lost when a stamp is soaked off its cover.)