Hello there, Shadowkitty!
Welcome to Feral Heart.~
Since you are wondering how to put something as your signature, I'll tell you. :3
Go to your profile on the forums and then click Forum Profile Information on the sidebar.
Scroll down a bit, and the box right above the last box says Signature, there you can post the link to your signature.
After that click Change Profile and you should have a new signature.
To change the size of a screenshot or picture, go to a photo editing site, like Photobucket.
Upload the photo and then edit it to the size that you want. :3
Would love to see you in game sometime, have a nice time exploring Feral Heart! c: