Symbol 2628 from ISO 7000 - Title/Meaning: Fuel cap unfastened 
Function/description: To indicate that the fuel cap is unfastened or not properly sealed.
Own work using: iso.org/obp/graphics/grs/14501b9f-77fa-4f3c-a318-01b67de9323f 200.png
Vectorization:  Mrmw