Hook: Wall Small (Green Square)The Circular Sign: Trooper decoration fits into a small green square wall hook.
Hook: Wall Medium (Blue Square)The Circular Sign: Trooper decoration fits into a blue medium square wall hook.
How to Get a Circular Sign: Trooper Decoration
The Circular Sign: Trooper decoration can be gained by completing the Chapter 3 storyline for this class, which ends right before Ilum.
If you have finished this storyline and do not see this decoration on your available list, open up your Legacy panel and go to your Achievements. Go to Achievements -> General -> Chapter 3, once Chapter 3 is open click on your class symbol. There will be an icon of a decoration in the bottom right: right click it to add it to your decoration list. You can right click it up to 50 times to gain 50 copies of this sign.