User blog comment:SlyCooperFan1/Kono Might Be Teasing Us, Again/@comment-3083606-20150819205825/@comment-1824272-20150821024347

I thought it was something like a file extension, but unfortunately p3n isn't a known file extension. p3t is one, though, which is the file extension for PS3 themes, which is why my assumption happened since I used to make my own a while back.

Unfortunately, since p3n isn't a file extension (which would make some sort of sense in that context Kono put it in), I have no idea.