Off Topic What’s this knife/sheath sitting on?

It's some sort of hard plastic or rubberish material. Like I said, it's a weird one. Ma has an office in the village too, and they left the top of that one sticking up in the way of the snowplow. We've already broken a couple, plus it's right where I park the 16 ton bucket truck, not exactly a well thought out situation.
Believe it or not, my first thought was a sewer or manhole cover like we had in NYC growing up...but when I saw that nipple or plug or ring in the middle, I figured it must be plastic and nobody would ever have a plastic cover for such...which is why I didn't opine after saying you had finished whacking the weeds.