The sign for
"balloon" is done in ASL by miming the action of blowing up a balloon.
BALLOON:

Discussion:
The "noun" form of the sign BALLOON is done smaller and quicker than the verb
form. The verb form is done larger and (a bit) slower -- as if you were actually
blowing up a balloon. The sentence will also provide context. If you use a sign
like HAVE or MY prior to the sign for BALLOON it will be fairly obvious that you
are talking about the thing and not the process of blowing up a balloon.