Following livius's Firefox and Emote Rips journal and Smiley Xtra Add-on to Credit Artists news article and the comments that they generated, I had a quick look at how many of our emote GIFs were actually signed. Out of about 400 I checked only two had a comment that named the author.
First a quick bit of history: There are actually two published GIF standards, 87a and 89a. The 89a standard introduced the multiple image handling that is needed for animated GIFs, plus support for a number of other features including text comments. These comment blocks are not part of the displayed data, they are intended for information only. A GIF file can contain any number of comment blocks with each block holding up to 255 characters. Note that the Properties/Summar