With great thanks to print scholar Dr. Roman Carbon, University of Erlangen, Germany:
"Hermann etched letters and numbers: 'radiert 1900/überarbeitet XII 1905' which means: 'etched 1900 corrected and worked across in Dec 1905' [XII is the roman writing for 12 and means December).
You could find this etching in the collection of Struck's artwork (by Jane Rusel, Frankfurt 1997) as the number 10R and the title ALTER MANN (=OLD MAN). There is also written down the edition size of 150. This work is also listed in the old collection catalogue of Fortlage & Schwarz as No 10.
At the Leo Baeck Institute NY online service you will find the piece as No 78.1605 and No LBI 2011.005 and it is numbered as copy 146/150. On that piece it was written verso by Hermann: No10 KOPF EINES ALTEN MANNES (=head of an old man).