That's an odd duck!
Colt commercial slides that were militarized received the "P" mark. However, it should be a parkerized slide to my knowledge.
The photos seem to show stipling of some kind on the top of the slide and the photo of the right hand side seems to have a gentle curve on the side flat forward of the ejection port, but that just may be a trick of the camera. This could be a refinished slide with a custom rollmark on the right side.
The 9m/m stamp is curious too; I've never seen the m-slash-m
Around 1935, a recoil plate was installed on the breechface. I'm not sure if I can see that or not in the photo. I think I do but it's hard to tell
The hand-stamp numbers under the pin retainer is likely normal for s/n range
My Clawson 'little book' (Service pistols, not commerical models) records that for military service, 856101-958100 were duplicate numbers manufactured by Colt, and that took place in 1941. However the reason for the duplication is not given, and I don't have the 'commercial' book to see if those duplicates were because of militarized commercial models. Colt did take commercial models and make them military models during the war but I do not know the s/n range
The guys at M1911.org would know more; I'm a knowledgeable amateur