Actually, I find that reference is rarely added at all on German notgeld.
It is not denoted in the catalog actually (as such). The issue is numbered just using numbers (88.4), and then below the example picture for the series, you'd get a list of different images/text that identify the notes in the series: (1. Kriegerdenkmal Rodewald, 2. Mandelsloh, 3. Seemann, …), so the notation -X/Y is constructed using this information.
The most common is just having a numista number, and then, on each variant, there's some reference in the comments using a different notation - typically like this: GrM 88.7-5/5 or such like.
Given that there's a reference on the note and a reference on the variant - having the reference in the comments must be plain wrong though, so suspect some fast and efficient copy/paste being done when adding the note here. Which is fine though - there's a lot of notes needing to be added - and getting the note added without all the bells and whistles is understandable.
I'm fine with keeping the style of -X/Y to denote the note number in the series in the reference field on the note - but it should not be necessary in the variants perhaps.
Reason I ask is that there's no clear precedent to follow here. The one precedent that's there with “GrM:88.4” in the comments on the variants is clearly “wrong”. Guess it is for Silberschatz to decide as notgeld referee.
