An icon from gnome-themes-extras-0.9.0.tar.bz2 (specifically Nuvola/icons/scalable/emblems/emblem-important.svg) by David Vignoni. 
Edited to look more like the PNG file by Bastique.
gnome-themes-extras-0.9.0.tar.bz2 (specifically Nuvola/icons/scalable/emblems/emblem-important.svg)


			
			Nuvola apps important.png
Bastique