Need ID for IBM Cards

I was just going through a box of old files (circa 1970) that my office is throwing out and I found four cards that I need an ID on. They are the same size and shape as a standard puch card, but appear to be made of some sort of magnetic media. They are approximately the color of standard magnetic cassette tape on one side, and nearly black on the other. Each card has "IBM" printed on it in white with a direction arrow next to it in one corner of the card directly opposite the notch. In the corner with the notch there are two groups of 3 digits, also in white. The cards have what appear to be track marks on them in three parallel rows on the horizontal, as if fed through a reader. Thanks. If it would be useful I post a scan of one of these.