check out http://www.pafoa.org. There are about 2 dozen regular open carriers in Philly - me included - we had a open carry dinner at Famous Dave's restaurant 2 weeks ago.....
I OC'd at the Island Ave PA DOT in SW Philly yesterday when my son took his driving test. Had a Phila PD Airport officer behind me in line (getting her drivers license photo updated) - she couldn't have missed the S&W M&P .45. Since I was in shorts and a green golf shirt I couldn't have been mistaken for a LEO. No issues.