I have an equipment card that has both a turret symbol and secondary weapon / missile symbol on it. I knew it was a misprint because they are 100% overlaying each other. That is the only part of the card that's abnormal.
Your "blank" sounds like the card never got printed with an image, and somehow was probably attached to the card in front of it in some way by a defect in manufacturing process. Then, adding to the infinitesimally small chances of things like this happening, it also got past the blue dot QC'er. I'd hang onto it as a good luck charm.