I have been researching this issue lately as well.
It seems some states specifically mention having a firearm while some don't.
Example of Ohio
http://codes.ohio.gov/orc/2911.21 vs
Florida
http://www.leg.sta...tions/0810.09.html Is there a blanket federal law that mentions this?
I know that if you were to get caught it would escalate the situation and you wouldn't get a warning, but my main concern would be a felony over a misdemeanor and not being able to legally own a gun again.
And what about areas you could accidently be trespassing, such as park instead of a factory?