oval heavy tin bass pale ale sign

Sign measures 16 inches high and 13 inches wide. Top of sign reads "this tablet is an enlarged copy of the bottle labels issued only by bass, radcliff and gretton". Bottom edge says" burton on trent & london ". Very bottom edge reads chromo-fulcent metalline. Any input as to value or rareity appreciated. The back of this sign was used for an oil painting. I just happened to notice the sign under the cardboard backing while i was looking at the painting.