Symbol 6035B from IEC 60417 - Title/Meaning: Press and hold; long push Function/description: [To provide information for the specific control that shall be pushed in, and held continuously, until it completes the intended operation.This symbol should be used in combination with supplementary text to explain the corresponding function.]
Additional information: 
See also alternative symbol 6035A.
Own work using: iso.org/obp/graphics/grs/288237ff-9913-490e-8536-51a86e25f178 200.png
Vectorization:  Mrmw