This is one of the original prototype HRSI tiles that was attached to the space shuttle Enterprise for the approach & landing tests. This tile came from one of the engineers who helped design the thermal protection system for the space shuttle orbiters. He removed it from the Enterprise after the ALT program was completed.
I've spoken with a few people about this tile and have been told that there were 10 of these prototype tiles installed on the Enterprise. They were all marked VT-70 engineering test and from the brown felt material attached to the white backside, it was attached to the vehicle, but I don't know where it was placed.