As far as I've been able to determine, a plant badge would literally be a twig, with some crabapple leaves worn on the hat, or at the end of the banner, to identify yourself to other members of the clan. Plant badges were probably the earliest way to identify your clan affiliation (someone correct me if I'm wrong). Two guys walk up to each other. Each has a crabapple twig, or leaves on their hat or clothes, they know they're allies.