I would never go onto someones land without permission. When I was a kid we scrumped apples and boy were we in trouble when we got caught. I learnt my lesson. Picking wild fruit growing adjacent to a footpath is ok but going onto someones land to take it is not.
My last place had a public footpath alongside one field, separated by hedge. The one time I caught someone walking on my side of the hedge so I called her over and pointed out that she was on private land and there was a footpath. Her reply? "But it has got muddy puddles" (yes, she had wellies on).
Next, I put new gates on to show that the field was in use (neighbours sheep and my horses) and not abandoned. I chained the gates shut for security, but then my NEIGHBOUR undid the gates by lifting them off the hinges (old bag) and left them wide open, so I chained the hinge side up too and chucked her sheep off my land (it wasn't the first time she had proved to be a pain in the ass).
Entering this field is free.
The bull will charge you later.
I love this, I'd put that sign up regardless of having any stock in there!