They can be identified through these traits:

For this type of hero, doing good for them is as natural as living and breathing. Not for themselves, but for everyone that lives in it. Opposed to what you would think, being pure good doesn't mean being a perfect, flawless hero. Pure Good means that these heroes want to make the world better, or at least keep it from getting any worse. It is the direct opposite of Pure Evil (a villain who is the evilest and depraved, without being redeemed). Heroes who are Pure Good, also known as Pure of Heart, are the best of all heroes, a hero who is completely pure and incorruptible. I swore that's what I'd become and I never looked back. I wanted to be a light as a beacon of hope. So, I ran towards that goal at full speed. I thought this country needed a hero who can inspire them.

I'm not certain how to explain it to you. What is the Symbol of Peace? That's tough. ~ Samurai Jack: in Episode 6 'Jack and the Warrior Woman'. My mission is noble, my heart is pure, I have nothing to fear.

Tvtropes sonic heroes