I saw this image today:
For the sake of this question, let's assume it happened in the front yard of the poster's house (so on his property)
If this really did happen, would this be considered a booby trap, because the nails served no purpose other than to destroy the property of people driving over the sign?
Would this trap be illegal, even though there's no way that it would reasonably hurt another human (if you're outside, you have shoes on, protecting you from the nails).
You cannot booby trap your property, see Can I booby-trap my property against police?
You can, however, protect your property in any reasonable way that will not cause harm to innocent trespassers. So things like fences with obvious barbed wire, road spikes that would damage tires but not people etc. From the images it seems like the nature of the spikes are such that they would injure someone who stepped on or fell on them and probably cross the line into booby trap territory.
