Provisional Protection.
I see the Smoking pipes page where the pipe came from and it's a beaut. There's something off here though. According to this site
http://www.chicagopipeshow.com/educa...y_Dunhills.pdf Only pipes made in 1917 had the Prov Pro stamping. It certainly would not be uncommon for Dunhills to have an incorrect stamp but that's quite a discrepancy.