A Zippy on speech balloons (a.k.a. speech bubbles, word balloons, etc.):
Where does the “almost 300 years” come from? Here’s the relevant part of the fascinating Wikipedia entry:
In Western graphic art, labels that reveal what a pictured figure is saying have appeared since at least the 13th century. Word balloons began appearing in 18th century printed broadsides and political cartoons from the American Revolution often used them.
Unfortunately, the link to “The Evolution of the Speech Balloon” that the article gives (and that you can find many places on the web) doesn’t work.
Some sample balloons:
From top to bottom: an ordinary speech balloon, a thought balloon, a scream balloon.