P&S are US military supplier which supplies M4 stocks and I've read around here also the KAC M4 RAS rail system and currently Colt is using their stocks on the CE1000 & CE2000 Expanse M4 carbines and other model carbines.
Most P&S stocks are identified by their cage code of 4U486 but there are some also have Colt's cage code of 13629, Colt started to use P&S stocks on their carbines production back in October last year.
The difference of the exterior mold line are very minor and hard to see, there is a vertical crease line about half an inch back from the front edge at both left and right sides, and at about half inch forward of the rear end there are sharp radius on top of the stock, with the older Colt stocks those crease lines and sharp radius are blended and smooth.
The surface finish of the P&S stocks are also slightly more glossy while the older Colt stocks are more dull matt finish, not glossy.
I've got two old Colt M4 stocks one made in 2010 and another in 2011, also a P&S marked with their cage code (no Colt cage code) from my CE1000 Expanse M4 carbine I bought new last March of this year.
Here's an old archived thread with pictures of both old Colt and P&S stocks.
http://www.ar15.com/forums/t_2_29/273863__ARCHIVED_THREAD____Picked_up_a_Colt_Expanse_today.html&page=1