5c Beacon on Rocky Mountains top plate block of eight
Top margin plate block of eight 5-cent air mail stamps; plate numbers 19546 (vignette) and 19551 (frame); letter F printed twice in vignette and frame colors; word TOP printed in vignette color.
When a plate was hardened, or “finished”, an “F” was punched to the left of the plate numbers on the right-hand side of the plate. The “F” was either 2mm or 2½mm high. The “F” was “punched” onto the plates, not engraved. When the plates wore, deeper impressions began to show a circle around the “F”.