the high sign
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A hand gesture used to signal someone about something. Sometimes, it refers specifically to the "OK" gesture (when the tip of the index finger and thumb touch, forming a circle). I'll give you the high sign when it's time to come out on stage.
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.
*the high sign
Fig. a prearranged signal for going ahead with something. (Often refers to a hand signal or some other visual signal. *Typically: get ~; give someone ~.) When I got the high sign, I pulled cautiously out into the roadway. The train's engineer got the high sign and began to move the train out of the station.
McGraw-Hill Dictionary of American Idioms and Phrasal Verbs. © 2002 by The McGraw-Hill Companies, Inc.