What is the current state of the law on trespassing on private property?

2 A person may go onto the property of another for the sole purpose of ascertaining whether the latter would welcome the former's noncommercial message at that location. (Martin v. Struthers (1942) 319 U.S. 141, 63 S.Ct. 862, 87 L.Ed. 1313.) However, once the outsider is aware he is unwelcome on the property, he has no right to remain. 'A city can punish those who call at a home in defiance of the previously expressed will of the occupant . . ..' (Id., at p. 148, 63 S.Ct. at p. 866.)