In today's electronic world, it's not difficult to identify "public" land. I was taught that someone will own a property, and if that person has not given me permission, then stay off the property, whether it's posted or not. This should be common sense.
There is a lot of un-posted lands in my area and most do not have fences. Common sense should say stay off those unless they are public, or permission is given otherwise. Not too far from my house is a tract of land owned by the Santee Electric, ( CoOp and also owned by the state) that is public hunting land, yet requires permits to enter. There's plenty of public land in my area.
Most of this type of information is available if you search for it. If you go onto private property and get caught, you deserve whatever consequences are involved. If you go to an area you are not familiar with for hunting or fishing, your fault is that you did not prepare! No excuse for that!
I once had waded up a stream in MD and a landowner approached me, stating that I was trespassing. We discussed it, civilly and agreed that as long as I stayed in the water, I was on state & public land. Not everyone will agree with that, as I have had it happen before on other streams, but I also agreed not to come back, just as a matter of keeping in good graces with that fellow. He was pleasant enough as we talked awhile, and had said he had problems with trespassers hunting & vandalizing his property. A very good reason that many land owners take the position of keeping others off their lands.
So, either make sure or don't risk it, or find out well in advance and get permission. This is not difficult to do!
I have read that purple paint is used in some places too in the same manner as the orange paint in trout trekker's post. I think I had read that WVA is such a state.