YOU FOUND THE RIDDLE.

SOLVE IT IF YOU CAN
TELL THE BARTENDER YOUR GUESS
AND UNLOCK A SECRET COCKTAIL

“I'm a silent promise when we meet,
A friendly gesture, smooth and neat.
Though I say nothing, I make a start,
Bridging the gap, connecting hearts.
When neighbors cross paths or strangers greet,
What am I that makes the meeting sweet?”

What am I?