Symbol 5031 from IEC 60417 - Title/Meaning: Direct current Function/description: To indicate on the rating plate that the equipment is suitable for direct current only; to identify relevant terminals.
Additional information: 
Published in: First edition, 1973
Own work using: iso.org/obp/graphics/grs/3fb20d13-a7e7-4e6a-8405-9cad255bff27 200.png
Vectorization:  Mrmw