Green’s Dictionary of Slang

to arrange one’s hair in a Rastafarian dreadlock style.

1991		Source Nov. 34: I don’t want to lock my hair.
2001		Atlantic City Press 12 Aug. G4: Employees who lock, braid, twist, bead, or ’fro their hair said they have wondered whether their styles might affect their ability to get hired or get plum assignments or promotions.