Symbol 3889 from ISO 7000 - Title/Meaning: Display test, off 
Function/description: To identify the control that switches off the display test function. To indicate that the display test function is inactive.
Own work using: iso.org/obp/graphics/grs/c235006d-9f29-4c9a-a0dd-1c13a4a8390e 200.png
Vectorization:  Mrmw