To set all of the balloons in a drawing, go to Options > Document Properties > Annotations > Balloons. You can set the Style to Triangular, and if you choose Custom Size in the Size drop-down you can make the triangles whatever size you want. You can over-ride these settings for individual balloons by clicking on the More Properties button at the bottom of the PropertyManager with the balloons highlighted. There is also a button there under Leader that you can click to hide the leader.
Here is an excerp from the help file that describes what Glenn is talking about.
Glenn and Scott,
Excellent info, thank you. Is there a way to change the aspect ratio of the triangle as well?
What if I wanted to make a custom-drawn flag of any shape I wish?