I will never have that problem but it would be tough to actually prove conclusively, even with pictures and gps. The pictures would be pretty good evidence, though. If it really bothered me a lot, I would probably just self regulate to the more stringent limits.
People I know who fish Federal waters, don't stop and continue fishing in State waters on return. Straight to the dock. Like previous post, would be easy to challenge a charge, but thats done in Court often...and just not worth the effort and time involved.
What fish are you talking about? its rare that state is greater than federal and if federal is greater than stated you just don't go in federal waters. Really what fish are you worried about?
grouper looks the same but I would say there is just no way to prove it. Like me buying a bag of weed ( which I don't smoke it) when I elk hunt in Co and then bringing it back to Fl. Was legal there but not here. If you talk to game and fish would love to hear their reply.