He/she probably drove the nails like that to prevent winds from ripping the sign off the tree....
Still nice to know that even though private property they allow you to fish there as long as your not an A$$
I know the story behind that sign. The landowner had a trail cam stolen by a fisherman. The area was then closed off to fishing for a while. The guy that float stocked that area finally got the landowner to reconsider and allow fishing again. Any more incidents and that area will be closed for good!
Best sign ever!! There is a place by us that a youth derby is held each year. And 150-200 kids take over the land it is left as it was found. The following week the adults destroy it and leave trash everywhere. Pathetic. I spend a day picking up garbage each year so we can keep the spot to hold the derby.