lol this should give you the answer..
"The "p" stands for "potenz" (this means the potential to be) and the "H" stands for Hydrogen. So you must write pH with a lower case (little) p and an upper case (capital) H. Writing PH would mean a public house! Writing Ph would mean philosophy as in PhD which means a Doctor of Philosophy."
Source : http://www.purchon.com/chemistry/ph.htm