The Gaming Table (5th Ed.) list two different white Square in Circle mold chips with a P in a circle. There is a third one with a denomination on the back of the chip. No font is listed, so it could be either (assuming no denomination on the back).

One was shipped to Midwest Game Supply, Kansas City, MO in 1954 (other chips were brown).
Other was shipped to Shannon Pratt, Portland, OR in 1970 (other chips were green, orange, and black)

Hope that helps.