Letterers are staff at Sonic the Comic who write the speech bubbles and words within them once the artists have completed the script. Most are distinguished by their unique fonts. STC had 3 to 4 regular letterers, with a few other contributors.
List of letterers
Sonic the Comic Online
On many occasions during Sonic the Comic Online, artists of particular stories would provide their own lettering. In fact, the vast majority of STC-O letters have contributed elsewhere as either a writer or artist.