The poker chip logo provides an icon as well as being a logo; I 'vote' for sticking with the original. The problem with using big letters PPA - is that the PPA is also the Professional Photographer's Association, which is a big organization and has been around many years. The current PPA logo - Poker Players Alliance, does not invoke the photographer's association as it is, whereas the logo 'anyhero' suggested does.
My father was a professional photographer and member of the PPA for many years, so I automatically think of it when I see PPA - especially in big, bold letters. Stick with the poker chip, and the spelling out of Poker Player's Alliance. I have had many people comment on the t-shirt I wear I got with my membership. Thanks for allowing my input.