A polite way to talk to a man, like 'mister'.
The word 'signor' can make people think of old-fashioned manners or of speaking in a fancy way.
Examples:
Good morning, signor.
Signor, can you help me?
The signor is very kind.
Excuse me, signor, do you have the time?
The signor always wears a top hat and a monocle.
The signor tipped his hat and walked away.