If it was glazed and fired inside ( mine is) a bomb couldn`t scratch it !! That is surely a possibility if you live in that area !! My 60+ eyes can`t make it out either !! But here is something you can try,, dust powdered sugar over that mark then dampen your finger and tap the top of the letters to remove the sugar !! Just from the top,,,see if the outline of the letters with the white behind it stand out better !! Let me know what you find out !!