Possible Clues:

• Tank top openings
• Members' entrances
• Flaw in insignia, which should not be part of a straitjacket
• Vest openings
• Where sleeves are attached
• Pillowcase dress' lack
• Openings for members? New role has to accommodate opening for member
• Openings for upper members
• Poncho's lack
• Vests have two