Where is indirect characterization about Romeo found in the story?

See below! :-)

There is plenty to be said about what is revealed about Romeo's character through what others say about him and what he says about him.

In the first act is where we get lots of Romeo's characterization, starting with how Romeo's father says this:

"Many a morning hath he there been seen, With tears augmenting the fresh morning dew. Adding to clouds more clouds with his deep sighs... ...Away from the light steals home my heavy son, And private in his chamber pens himself, Shuts up his windows, locks far daylight out And makes himself an artificial night..." (1.1)

He's worried about his son, and how awfully sad he is. This already gives the audience an idea of what Romeo's character is going to be like, since his own dad claims that he cries and sighs and locks himself in his room and sits in the dark. This speech alone helps to develop who this character is.

Next, I would say another good part to seeing what Romeo's character is like is found in Romeo's own words. One thing I believe stands out about Romeo is how he exclaims quite a bit -- it shows the audience that he has a bit of a flair for the dramatics.

"Ay me!" (1.1.185) (This is literally the second sentence he says in the whole play)

"O me!... O brawling love! O loving hate! O any thing, of nothing first create! O heavy lightness! serious vanity!" (1.1.195)

"O, teach me how I should forget to think." (1.1.255)

Already with these tiny details we know so much about Romeo, and it's all so indirect and subtle! Shakespeare is showing us how Romeo is instead of telling us. It's easy to outright say, "Romeo is a sad, sad little man.", and a little more on the tricky side to go, "He has been wandering around and sighing all day" and have the audience pick it up just as well. Not to get off track, but Shakespeare is amazing, you guys.

Anyways. Are these examples good enough? Would you like more? Get back to me! :-)