do not enter. (Usually seen on a sign. Not usually spoken.) The sign on the tree said, "No Trespassing." So we didn't go in.The angry farmer chased us out of the field shouting, "Get out! Don't you see the 'No Trespassing' sign?"
to intrude or encroach onto a restricted or private area. (Upon is formal and less commonly used than on.) You had better not trespass upon Mr. Green's land. I wouldn't trespass on that fenced-off land!