In Wyoming, If one side is public, the other side posted. Its posted to the middle bottom of the stream. I don't know about the markers either on all waters. In the Shoshone Forest, there are places that are posted up the hillside but very unclear on the stream. I am fishing to enjoy myself and don't want to be looking over my shoulder, if in doubt I'll either ask or play it safe. Suprisingly, a politeknock on the door or stop by when a rancher is in the field can still get you access. As a camp host outside the NE YNP, I've seen "overflow" from the Park on weekends come into the National Forest to fish, and trash private ranch property acting like they own it. The problem is that not everyone with a rod is a sportsman. I have a lot of fishermen come through my camp and I enjoy talking with them. I ,also, have had folks anglers or not, come in,park on an occupied (someone else's) campsite to access the stream. There is an overflow parking area and roadside parking a very short ways away. A couple of these characters may have caused the posting for us all. Sorry to say, sometimes the posting is to protect the landowner's property. If in doubt, ask or just play it safe.