2: Go to the "Account" page, as circled in red.

3: Find the "characters" portion of the page near the bottom.

4: Right click your character's icon, as circled in blue.
5: Chose "copy image url", or the equivalent option for your browser.

6: Next, go to the forum, as circled in red.
7: Next, click profile, just right to the wrongly placed blue circle.

8: Chose the profile tab, as circled in green.
9: Go to the edit signature page, as circled in yellow.
10: Insert image tags, as circled in pink.
11: Paste the image url for your player icon between the tags.
12: Hit save, as circled in black.
Now you have your player in your signature for all to see! Note: This sadly doesn't work for your avatar, as it doesn't recognize the link as an image. You can always upload your player icon to the forum, but then you need to update it every time the player icon changes, instead of having the changes automatically happen.
You can give credit for this tutorial to There is a Fox Outside My House That Will Kill Me So I Have Free Time co.