S&W Sigma question

[potmetal]

I saw an ad recently for a Sigma that was marked on the slide as a 40GP. It was green, which I'm sure is what the G stands for. What was the P for? I know, and have owned an F series pistol, and the VE, which is the newer model, I've never seen one marked with a P.
It was priced a little higher then a new VE model, I have no idea why.

 

[smalls]

Hmm, I couldn't find anything on Google. Where did you see the ad?

 

[Onward Allusion]

Blackened SS with night sights.