Hi, Carol. Contact Dumond Chemicals, the same nice people that make Peel Away paint stripper at www.peelaway.com. Ask Hy to send you all the literature on their anti graffiti system and for his comments on suitability. His literature does say not to use it on painted wood without testing but that's about all it says specific to wood. You might also choose to call him in NYC at 212-869-6350.
You're welcome, Hy. And Carol, if a guy with a Bronx accent calls you over the weekend, hang up or your whole day will be shot. LOL But I guarantee that it will be a fun call and you will learn a lot.