Symbol 1978 from ISO 7000 - Title/Meaning: Halftone/grey tone 
Function/description: To indicate function on document reproducing equipment for obtaining halftone/grey tone.
Own work using: iso.org/obp/graphics/grs/7aac347f-c7f0-4649-b1db-baf4e2ef6287 200.png
Vectorization:  Mrmw