Hi Gang:
This is a hidden booby trap. I see no warning signs and the "protective" domes are black, not blaze orange. Looks like England as the car is parking on the left side of the road. Are these put in by the city, or the local property owner? What about workers delivering materials and emergency vehicles?
In Iowa we had a farmer loose his farm for setting a booby trap in an abandoned farm house. Didn't hurt anyone, he was just caught setting it.
Carl.