This is the body buck tag, also known as a build tag, which was for body line use only during assembly. Buck tags were installed on late '65 through '71 Dearborn and Metuchen units as well as a handful of '70 San Jose units. San Jose used buck tags for a very short time. The buck tag contains the VIN, rotation number (upper left, the actual unit position on the line), and actual date of assembly code, color and trim codes, and a smattering of option codes. This information tends to be very inconsistent. The Mustang and Cougar Tagbook from Marti Auto Works will help you decode this information for '65-'73 models.