In many US states if there are NO "No Trespassing" signs, property owners can, or have the cops, tell you to leave and then you MUST immediately leave. If you don't immediately leave the cops can escort you off the property or more (ticket, arrest, both) particularly if you resist by putting up a fuss so mind the attitude. If there ARE signs and you get caught you can be fined and maybe arrested depending on what the property owner's or cop's mood is at the time. In my experience their mood is often connected to what your attitude is when confronted.

That said IMHO stealth camping is gambling with the odds in your favour