highsign/ high sign

Raymond ChandlerのTrouble is My Businessを読んでいます。
We went out to the lobby again and Hawkins took me to the elevator and highsigned me in. As the elevator doors closed I saw him on his way to the entrance, probably for his walk around the block.
"highsigned" はどんな合図あるいはジェスチャーでしょうか？　"high" が付くので手を高く挙げて合図をする様にも思えますがどうでしょうか、辞書を見ます。
辞書は "highsign" ではなく、"high sign" の二語での表現の説明しかありません。
・Oxford English Dictionary: A surreptitious gesture, often prearranged, giving warning or indicating that all is well: I’m getting the high sign from my secretary?gotta go.
・Collins Dictionary:(US, informal) a prearranged and usually covert signal to someone to tell them that they can do something ⇒ They gave me the high sign from the front of the house; the father and mother weren't home. So I had the run of the house.
なるほど、何か内密のあるいはこそこそとした合図のようです。具体的にはどんなジェスチャーなのか、又この語源の由来も知りたいところです。
語源は分かりませんでしたが、ジェスチャーについては俗語辞典のUrban Dictionaryに次の記述がありました。
Providing a non-verbal indication to someone that you are ready; usually ready to go or leave, or ready to do something. Can be done in a number of ways - high wave, thumbs up, point with index finger. You stumble in to a very boring party. You and your buddy both know that you want to leave. One finally gives the high sign to the other by pointing to the door. They leave.
納得です。