Refer to the documentation in the s_bubble.dm file for more information.
I created the smileys for the bubbles.dmi icon. However, the original creator of the speech bubbles themselves (and the symbols that are not smiley faces) remains unknown to me.
(If you know who made those icons, let me know and I'll give proper credit).
May 20 2001, 9:00 pm
Here are the bubbles you can use: