It would probably depend on how big your balloon sculpture would be.
Look at the first section of FAR 101 (That means Federal Air Regulation)http://www.flightsimaviation.com/data/F ... 101-1.html
They really want to watch out for big flying stuff, which is why these rules exist. (Most likely, your sculpture won't be an issue at all).
No idea where you live. Search the web for the FAA regional office near you. Talk to a Regional Office: not the local control tower.
Edit: And, of course, I didn't look at your picture before I wrote this! Again, probably not an issue, but talk to a regional office, especially if you are launching near an airport.