a gesture, glance, or facial expression used as a surreptitious signal to warn, admonish, or inform.
Origin
1900-05
Examples from the web for high sign
Wind vibration of a high sign is more likely to loosen up the post than a low sign.
Idioms and Phrases with high sign
high sign
A secret signal intended to warn or inform, as in Dad gave us the high sign when it was time to leave. This expression presumably alludes to a gesture such as a hand wave. [ c. 1900 ]