How does Tybalt recognize Romeo in Romeo and Juliet?

Tybalt knows that Romeo is a Montague by his voice.

Tybalt is very committed to the feud between the Montagues and Capulets.  He has a fiery temper, so it suits him just fine.  He knows every Montague, including servants, so it is not hard to imagine that he would know Lord Montague’s son.

Tybalt calls out Romeo’s cousin Benvolio out by name in the marketplace during the beginning of the duel between Montague and Capulet...

Tybalt knows that Romeo is a Montague by his voice.

Tybalt is very committed to the feud between the Montagues and Capulets.  He has a fiery temper, so it suits him just fine.  He knows every Montague, including servants, so it is not hard to imagine that he would know Lord Montague’s son.

Tybalt calls out Romeo’s cousin Benvolio out by name in the marketplace during the beginning of the duel between Montague and Capulet servants.

TYBALT

What, art thou drawn among these heartless hinds?
Turn thee, Benvolio, look upon thy death.

BENVOLIO

I do but keep the peace: put up thy sword,
Or manage it to part these men with me.

TYBALT

What, drawn, and talk of peace! I hate the word,
As I hate hell, all Montagues, and thee:
Have at thee, coward! (Act 1, Scene 1)

Tybalt has no problem fighting Benvolio, but Benvolio is trying to prevent a fight.  It doesn't work.  This one escalates, especially when the heads of the families arrive.  The marketplace fiasco causes the prince to make an announcement making all public feuding punishable by death.

Tybalt does not seem to care much.  As he told Benvolio, he hates all Montagues.  Therefore, he is not happy at all to find Romeo at his cousin Juliet’s party. 

This, by his voice, should be a Montague.
Fetch me my rapier, boy. What dares the slave
Come hither, cover'd with an antic face,
To fleer and scorn at our solemnity?
Now, by the stock and honour of my kin,
To strike him dead, I hold it not a sin. (Act 1, Scene 5)

It seems that all Tybalt needed was the sound of Romeo’s voice and he recognized him.  Of course he wants to fight him then and there, but Capulet stops him.  He tells Tybalt that Romeo has a good reputation, and he does not want a fight among his guests.  That would ruin the party!

The ongoing feud between the Montagues and Capulets is one thing, but both Tybalt and Romeo are at fault here. Romeo should never have gone to a Capulet party, and Tybalt should have left Romeo alone.  Since they both made mistakes, it led eventually to Romeo killing Tybalt even though he never wanted to fight him in the first place.