The one pictured does look like a municipal manhole cover instead of one belonging to AT&T or another communications company, just because of the design on it.
That was one thing I could never do when I was an "urban explorer" (fancy term for trespassing in to municipal water infrastructure), manholes always freaked me out so much my friends couldn't even peer pressure me.
I was under the impression that the grates which don't have a city name are older from a time before people realized that they can be stolen and sold for the value of the scrap metal.
Then municipalities started to stamp their name on it and metal recyclers couldn't take them anymore unless you took it to a shady recycler so the value dropped.