Three good signs that Young Goodman Brown (YGB) is the protagonist of Nathaniel Hawthorne's short story "Young Goodman Brown" are as follows:
1. He is the central focus of the story. As readers, we experience all the action as it relates to him. We stay with him throughout the entirety of the story. When the traveler in the woods outside of Salem leaves YGB's side, we don't follow him. Instead, Hawthorne always keeps us alongside YGB.
2. The omniscient narrator focuses attention solely on the inner workings of YGB himself. Although we see YGB's wife, Faith, at the start of the story, we remain outside, observing her actions, rather than experiencing them through her. With YGB, we are given insight into his inner thoughts and emotions.
3. The entirety of the action happens to YGB. He is the one who goes on the journey and is changed by his decision to do so. He is the character that has the opportunity for redemption and chooses not to take it at any point in his journey. Beyond his initial interaction with Faith and his subsequent withdrawal from the community at the end of the tale, his actions are things that can be said to have truly occurred; every character interaction in the woods could have been part of a dream he was having. He is the one that ends up doomed.
For these reasons, and a number of others, Young Goodman Brown is clearly the protagonist of "Young Goodman Brown."