When I saw this at the thrift shop I assumed it was a piece of Fire King.  I couldn’t get a good photo of the marking, but it is the letter “F” in a shield and the words “HEAT PROOF” and “U.S.A”.

It wasn’t until I was poking around the usual cast of sources for an identification that I discovered that it was made by Federal Glass, likely in the 940s/1950s.  Seems to be lots of pieces available for purchase.

Don’t know where this will end up, but I only paid 25 cents for it.  It may go back to thrift shop!