Among the special units various Kappenabzeichen of military hospitals will be uploaded. Other sanitary badges depicted special jobs of medical care. But there were also the well known red cross symbols. Sanitary soldiers on the field usually had white armbands with the red cross. but there were also badges depicting solely this symbol. As is known, the red cross symbol was introduced after the 1859 Solferino battle, thus by the time of the great war it was widely used and understood.
I attached three different badges to this photo of sanitary soldiers. Maybe there were many other variants. In another post we can discover a nurse wearing a large red cross badge. Thus, these badges were most probably universally used by members of the health troops. It is worth to know that there was also a sanitary badge version of the regular qualification badges (Tätigkeitsabzeichen). The badge was awarded to personnel which spent at least 6 months duty in infection hospitals and did his job satisfactorily. Contrary to these badges the smaller more simple ones could be purchased by anybody interested.