Fonts

Hello fellow T-shirt Forum posters I am new to this website as you can see my posts are very low anyways I had a quick question that I am sure has been answered already please forgive me if it has been. Here is the question I am starting a clothing line and I am using several different fonts that I find on the internet. Most of them are free but I have noticed some of the fonts like this graffiti font I downloaded has a copyrighted I am using this font on my shirt although I am not saying that I created the font or passing it on as my own what are the rules when making T-shirts? Could this person sue me? I am not using any of his names or passing his fonts as my own but I am using the font on one of my shirts and selling them. Please let me know all the rules thank you.