Well a group build badge is just a token that one has been involved or has successfully participated in a particular group build. Like when we were boy scouts, we earn badges for certain accomplishments. There is no rule about the group build badges and wearing them is up to the group build member. I would assume however, that it is only proper that only members of the group build are entitled to wear its badge.
So far there are two group build badges, the Sherman Family Group Build and the Panther Group Build badges.
The other badges however are for everyone else unless of course the owner signified their exclusiveness.
The ones that I am using are for everyone:
1.) The badge showing tracks over a propeller is a token of the time when the armor forum has passed the a/c forum in the number of posts.
http://www.info.com.ph/~tdwight/Threadhead3.jpg
2.) The badge with a crashed A-10 is just a "fun" badge. Some of the a/c guys made fun of the original badge and the crashed A-10 is the answer to that.
http://www.info.com.ph/~tdwight/a_10down.jpg
3.) The badge showing a sprocket with tracks is a sample badge for all armor forum fans / members.
http://www.info.com.ph/~tdwight/armorbadge.jpg