I've searched near and far for a method and I finally figured it out. By typing /tell then clicking on the link your guild thing or shift clicking another guild you can see their ID or just view their page on the official site and look at the url for:
https://realmwar.warhammeronline.com/realmwar/GuildInfo.war?id=838&server=166
This is the Guild's ID. Now Use the information bellow to link a guild.
<LINKdata="GUILD:[GUILDID]" text="[CHATTEXT]" color="[RGBCOLOR]" >
Where:
[GUILDID] = The Guild's ID Number
[CHATTEXT] = Normally is "[Guild Name]" but you can set it to anything you like. Even "We da' best d'm guild there is yo".
[RGBCOLOR] = The color you would like to use formated as so: R,G,B each one is from 0 - 255. So Red Would be 255,0,0. Blue would be 0,0,255. I use: 243,228,103 in my macro as it is a gold color and not the standard color. For more colors see:
Color Picker