Being a property owner that has dealt with people looking for native plants, - digging them up just because they were "in the middle of nowhere". They were not in the middle of nowhere - they were in the middle of my property! I think everyone should think twice about tresspassing to basically steal plants from other people's property. How do you know that the owners of that property aren't also waiting to harvest THEIR fiddleheads?
For anyone with concerns about folks trespassing on their property (for any reason): Post signs every 20-50 feet along the property line -- and especially at every easy-access point! Official, legal, weather/UV resistant signs are available at every decent hardware/home improvement store (Menard's, Lowes, Home Depot, Walmart, the local hardware store, etc, etc, etc) and cost around $1 each. If someone ignores the signs and trespasses anyway, you can have them arrested.