There is no universal notch code.
Years ago, when Kodak was still the 500# gorilla in the industry, they started a trend to coding individual films with distinctive notches involving a combination of shapes and their sequence. Unfortunately, the only industry standard that evolved from that practice was that the notch should be in the upper right corner when facing the emulsion side of the sheet.
I believe that Kodak still uses distinctive codes on their films. Here's a
link to the most recent published definitions that I could find. Unfortunately, the notching on Sirius Glass's sheet doesn't seem to match any of those codes. Note that Kodak appears to use sharp corners on rectangular notches, while Sirius Glass's notch has rounded corners.
I think Richard's example only shows one corner of the sheet. But clearly it doesn't convey much information. The only suggestion I can make is that the shape of the notch reminds me of the notches in Ilford film, but I can't get any more definitive than that.