Thank you LeeD! I’m guessing it could be a tag for the cab number while being built in a specific factory, and prior to being installed on a vehicle with a serial number.
1957 Chevy 3200Daily DriverPS, A/C, Tilt column, Rebuilt 350, Rebuilt TH350, Reupholstered Bench Seat, sound proof/insulated, LED headlights/taillights/backup lights/interior courtesy lights.
Follow in the DITY 
