I traced this one with a pen and got two squares (minus one side, of course) and nothing else.
Kind of like this, if you put straight bottoms on the notches and flip it upside down:
__| |__| |__
I have thought about it, and perhaps it is the piece that I found in that one old holder I got when I purchased that fridge full of very old paper for $20. In that case, it could be VERY old (anywhere from the '40s to the '80s)...and probably b/w.
If this is the case, it is probably nothing but black. If no one can identify it, I will slice off a small corner just to see if it is b/w or color. If b/w, I will try just for the hell of it.
Here is what I have so far, from a 1961 photo lab index (now that I suspect that the film is old, I took a look)
- DuPont Cronar Arrowpan matches perfectly. ASA of 320 makes a 100% black piece of film about 100% likely.
- Gevaert ortho emulsions all had this code...but also had a hole in the corner for hanging, which I did not notice when tracing the notches.
- No Kodak notch matches.
Unfortunately, these are the only companies for which notches were pictured.