Eine Möglichkeit : SM - staff member
http://www.acronymfinder.com/Staff-Member-%28...

SM may work if needed, but be aware that English doesn't tend to abbreviate such terms nearly as often as German, and it's best if you not do so unless necessary. For example, English would not use "SM" in a document in the same manner merely to avoid writing out "staff member" in the same way that so many German documents will include "MA" when, truth be told, there is no compelling reason for using that abbreviation at all.
A case where such an abbreviation might be used in English: "SM" as a header of a column in a table where the caption of the table makes the term clear, such as "Table 1: Staff members working at home"
My general rule (also requested by major clients who care about style...): Just because the German text includes an abbreviation it doesn't mean that the English text should or can include a matching abbreviation.

Vielen Dank für eure Antworten!

@hbberlin: you're absolutely right, I should have made clear that I need this term for a table.

I'll think about your suggestion once again and then decide, if I will use the term.

Thank you all and have a nice day!

Julyfox