Creating your own signature is quite simple. Type in your character's name and then choose your realm from a drop-down list. Upload a photo, or opt to stick with the default that the computer will find for you. You can select one of twenty-two different backgrounds, and you can change the font colors for the various stats displayed. Although you cannot see your character picture in the preview window while editing, everything else is visible, allowing for color coordination.
By default, your signature will show your character name, guild affiliation, class and race, talent build, and professions information. In addition, it will display up to seven other attributes of your choice, from lifetime honorable kills, to spell crit, to faction reputation.
Of all the features, my hands-down favorite is that you can upload and use your own picture of your character. All you need to do is set up a photo-shoot. Create a cool costume, pull out your craziest looking weapon, hop on your mount, or simply snap a shot of yourself staring blankly back at you. Open your screenie in even a basic photo editor, crop it, choose "square" when entering a proportion, and voila! You are an instant signature-star!
When you've clicked submit, it will show you what your signature will look like and allow you to edit it. It also provides the link to the image hosted online, and the html code and BBCode, with and without links, although you can also save it to your computer. Just insert the code into the signature box when you write a post (it will remember it for the future), and you have yourself your very own armory signature.
Update: Yes, we have talked about this before. In light of my recent discussion about addons for those who are uncomfortable with them, ongoing improvements to the armory, as well as increased usage of it (and considering our first mention was in March), I thought it deserved another mention.