|Signature: Why ?|
is pretty apt as a signature - it is short, it is significant, it is unique, and it is in line with tradition: Rembrandt and Vincent among others used their first names.
Well, Werner Stürenburg doesn't use his first name Werner but rather his student nickname Joe which he acquired in reference to a whim of American immigrants in Paris described by Henry Miller. At that time, he was Joe and signed accordingly, using small letters only.
In another way Joe as signature ist significant also. As related by James Joyce in "A Portrait of the Artist as a Young Man", with this nobody-name the artist steps back as a person and lets his work speak for itself.