Our troop is having our Investiture Ceremony Saturday and I need to make cupcakes. I am drawing a blank as to how to decorate them. Ant ideas would be very helpful.

How about merit badges:
http://goshop.girlscouts.org/GSUSAOnline/GSBasicLandingPage.aspx?subCatId=Awards-Girl11

There are lots of them and they are usually simple in design.

Edited to add: I made a cake for a Brownie Investature ceremony a while back. I was asked to copy the patch as the design.

http://www.sugarfrosted.com/displayimage.php?pos=-2320

You could do little girl faces of every color on the cupcakes.