Yes, totally normal in Germany. Flip coin of the story:
When moving to US, young German man finds himself using sauna in his apartment complex in one of the Western US states. Properly forewarned about American customs, he carefully studies the instructions outside the sauna. Yes, the little stick figures are only wearing a towel, so he enters and lies down on the towel. Next thing is two women shrieking and running out of the sauna, only to return a short time later with security, who are ready to throw him out of the apartment complex. His foreign accent rescues him --- lesson learned.
As an aside, I'm grossed out when I see people in their swim trunks sweating all over the sauna benches.