In most residential areas, at least around here, water shut off valves are covered by cast iron caps. All of the ones I have seen have a pentagon shaped bolt head. Some are an actual thread, others are just a cam/lever, holding the cap on.
It's supposed to be a security thing, though not highly secure. A simple pair of Vice-Grips can defeat it, but it looks like it's doing something.
I have never seen the proper tool for sale, even on tool trucks, not that I was looking. Then I found one, laying right on the side of the road. This pic is a bunch of random stuff I found cycling around town. I have been a bit lacking lately, but I used to commute to work along with regular exercise riding, putting down several hundred miles a month. The number of things falling (or being thrown) from cars, is surprising. Some of it is not safe to retrieve, some is pretty interesting.
Wrenches, screwdrivers, sockets, phones
Right near the middle is one of those pentagon sockets, must have fallen from a truck.