What the . . .?

Sometime while I was mowing in the back yard this afternoon something landed on our front sidewalk.

Below the 20 are the letters "hps"-- there is nothing else printed on it.

This metal item has a part of a latch at the top.  It is about 24" long.

The opening apparently had been covered by a piece of tempered glass because there were a million little pieces all over the sidewalk and in the grass on either side.  I cleaned up the shards on the sidewalk but it was impossible to take them out of the grass.  I hope no one gets cut by them.

I'm guessing it flew off something being transported by a passing vehicle.

Any clue as to what it is?