a rod about 5/8" diameter with a slot in the end .
Yep. In Texas, at least on the north side of DFW, there wasn't any kind of lock or anything to get into the shut off valve and meter. There was a cement cover over the little hole in the ground with a metal flip up panel which was something like 3" wide by 6" long. The tool I had, which I realized just today I left with my father in law when I moved to TN, had a little hook on the top for opening that metal panel and the business end was similar to what you see above.
There wasn't much room at all to get pliers or any other tool in through that 3" X 6" opening and twist the valve.
I probably haven't looked at it close enough but I think it's about the same here in TN. I also remember a very similar setup in Lawton OK when we would go visit my grandmother every year while I grew up. The neighborhood kids would go down the street opening the meter panels and looking for snakes inside.
Never did get to see a rattler but I was told they weren't too hard to come by. I know my grandmother found one in her washing machine once, which was in her garage.