Symbol 3305 from ISO 7000 - Title/Meaning: Unlock Function/description: To identify the control that effects an unlocking function. To indicate that the component or function is in its unlocked state.
pay attention to orientation of symbolAdditional information: 
Symbol IEC 60417-5570 may be used as an alternative.
Own work using: iso.org/obp/graphics/grs/9a7d9be8-9349-4353-b635-0da02a676449 200.png
Vectorization:  Mrmw