The Northern California Fly Fishing Board

Just did a trip down oregons coast and had the same issues. Basically I assumed if I didn't know it was public then its not. That way you are safe.

But how to tell public lands? Fishing regs on a tree are a good sign. Especially if there is a turn out with a path to the river. found lots of pull-outs with little yellow cards with regs on them. If you couldn't access there why would they put that up? Also the whole "access the river and don't go above the high water mark" rule works well. bridges are public land.
Probably the best thing to do is ask the local shops, specially for steelies cause they'll tell you where to find fish. Buy $25 worth of tying materials or leaders or something and they'll love you. You need that stuff anyway.

Where ya heading? Its friggin freezing here in mid oregon and I'm hitting the coast this weekend. Will PM ya ifn there aren't any Trinity type report! Just kiddin.