(source: Iceberg Slim - Pimp, The story of my life)

Section that contains the expression:

"We were at a cabaret. Carmen was behind a twenty-six game table in the barroom. I left my table and went to the John. I passed Carmen on the way. She gave me a strong lick."

Background:
Slim is at a night club. He spots a girl who looks convineable to be his whore. He walks close to the girl's table and she gives a sign to call his attention. But what she did exactly? What 'giving a strong lick' means?