There's actuly a code to horses used as insighnias. I dont recall how the code is but it has to do with the position of the horse (running, prancing, etc.) and the direction it's facing. I think a prancing horse facing to the right (from it's perspective not yours), like Ferrari's, is supposed to symbolise a victorious warrior. I might be wrong thouh, and I doubt the mustangs horse has any signifgance to this code.