Symbol 6444 from IEC 60417 - Title/Meaning: Maximum operating depth Function/description: To indicate the maximum operating depth for an appliance or other equipment immersed in water.
Additional information: 
“X” is to be replaced by an actual value depending on the needs, but it is bigger than or equal to 1.
Own work using: iso.org/obp/graphics/grs/bcb41b4e-809f-4d0f-a1b4-9157c14d9e3e 200.png
Vectorization:  Mrmw