Hey there!
To prevent spambots, and other potentially malicious accounts from adding items to their signatures, and just for a general go-to rule of relatively active forumers to have the ability to edit their signatures, you need to achieve 30 posts before you're able to add images, or links to your signature (basically what
Mooclan said
).
To check your number of posts, simple go to your profile (scroll to the top of the page, hover over your profile picture and name) and select the drop-down option "Your profile page" (next to your listed rank).
From there, you can find your messages, likes, etc. listed underneath your avatar, as shown in
Mooclan 's handy-dandy image:
You currently have 21 posts, so you're almost there!
Thread locked; feel free to contact me with any further questions- I'd be happy to help!