Instructions
Visit and talk to a guild master. Click "Purchase a Guild Charter." Guild masters reside in each major city.
Open your bags and right-click the guild charter, which looks like an envelope. A list of signatures will appear, with your signature listed under "Guild Master."
Click a character whose signature you wish to acquire and click the red "Request Signature." button. If the person signs the guild charter, their character name will appear in the list of signatures. You must click the character itself; you cannot select someone from a friend's list. Once you have four signatures from four different WoW accounts, return to the guild master and click "Register a Guild Charter."