Here's the thread:
http://www.silkroadforums.com/viewtopic.php?t=45939
HOWEVER, it clearly states in reK's post that that Request Thread is used for people requesting Sigs. I've seen Master requesting lots of non-Sig related things for SD, and they've all been open fine, so I think that you should just make the request here. I'm pretty sure that it's fine, and won't get locked.
If you had an idea of a guild logo that you wanted (an animal? a plant? a certain design?), it'd be a lot easier to make a logo for you. If someone's to do this for you, it's only polite that you make it as easy on them as you possibly can, since they're donating their own time to help you.
And congratulations when you hit L4.
