"Council of Thirteen"   "The Gathering of Clans", or "Clanrats"

This elaborate design on the left is the symbol for the Council of Thirteen. It is also used to represent the capital letter "C". See Skaven army book, page 49 ('Eavy Metal pages), on Screaming Bell miniature.

The symbol on the right, three over-lapping lines forming an inverted triangle followed by a series of overlapping lines below it of descending size represents the joining together of two or more skaven clans for a common cause. It is often found adorning the standards of mobs of Skaven of more than one clan, collectively known as Clanrats. See Clanrat banners, Skaven army book page 49, ('Eavy Metal).