Joker Balloons are part of a small challenge to pop a small, tied down (and together) group of balloons with devious smiles on them.
They are a lot like the TYGER Security Cameras, mounted objects that you must destroy for The Riddler's Challenges.
Batgirl: A Matter of Family Incident
Multiple patches of Balloons were string around Seagate Amusement Park. Destroying them all, along with Joker Teeth and Harley Quinn's Jack-In-A-Boxes are required for a achievement/trophy.
Arkham City Incident
Small groups of Joker Balloons are scattered around Arkham City. They are part of Riddler's Challenges and encompass bits of the Industrial District and Amusement Mile.
The Joker Balloons in Arkham City.
- The balloons can be popped with the Batarang, REC, Freeze Blast, or just by passing over them while gliding.
- Balloons also appear in Arkham Knight, but are purely decoration. They can be popped just like Joker's Balloons.