The Pegasus is a symbol of the shield with passant wings elevating argent a chief. The Quinn name is one of the top 20 most numerous surnames in Ireland, and it is the most numerous surname of Tyrone. Visit http://www.araltas.com/features/quinn/ for more details.
Good question. As my family, surname Dove, is DNA related to many Quinn, O'Quinn, etc around the world, and though from Scotland were also Gaels (common), both share a Pegasus as their crest. I found this interesting.