There is a long, thin, rubber-y line wrapped around/connected to the water line pictured below.
Other angle:
The piece in question is loosely hanging via a zip tie on my main water line about shoulder height and can be moved up/down easily.
If you go up to one of those covers and look at it, you'll probably find that the meter well is using a nonstandard bolt head (often five-sided) in an effort to prevent tampering. I bet that used to work a lot better before people could just buy any weird tool they wanted on Amazon (though I wonder if anyone cares now that water is such a tiny fraction of most people's monthly budgets).