Local regulations notwithstanding, if I had beehives located at a "pick-your-own" farm, I'd put signs up. People could wander too close without noticing the hives, just looking around...I've seen plenty of oblivious people. It could also be informative to the curious, enticing them to look but not get too close. I'm not putting them in my backyard; I have .19 acres, both my next door neighbors know I have bees and think it's cool. No one goes into my backyard except me and my wife. I have some hives on some farms, and I don't put signs there, either. The farmer knows they are there, and no one else goes there.