I am completely against riding where you do not have permission. It only makes all of us look bad, and fuels their fire for shutting down other riding areas. If you want to ride there, be an adult, go to the town, find out who owns the property, and ask permission.
Well said, although if an area is not posted and it's obviously being ridden, then I will ride through. But if you see posted signs, you should honor them. Likewise a gate, which definitely says "stay out". And of course if you've been told to stay out, you should.
Don't forget to point out (assuming your atv plated, which you should be) that you are carrying liability insurance when you do ask permission. Usually that's what most owners are fearfull of. Also point out that you will stick to trails and not ride all over the place, or places where they don't want you to ride.
I had one guy that didn't want me disturbing ducks in one area. As long as I stuck to the edge of his property, he was happy.
Jim.