Symbol 5570 from IEC 60417 - Title/Meaning: Unlocking Function/description: To identify on a control that a function is not locked or to show the unlocked status.
Additional information: 
Published in: Supplement N, 1995;3C(Central Office)192
Own work using: iso.org/obp/graphics/grs/3e3d2bc4-e5f3-46b4-be9a-751213a86555 200.png
Vectorization:  Mrmw