Sheluma

I thought it might be a round shank since it's German, and so old. But writing that made me think about where the hook catches the loop, and I looked at your picture of the underside of the machine. I thought the loop would be on the left and the groove should face the wheel. A light bulb went off -- could the note be about the groove?

The macron hasn't been used that way in a very long time, so I can see why a native German speaker would have a hard time deciphering it unless she knew about the long groove in machine needles.