Preferably no large images or text. Some members browse Lit on smaller screens and don't have fast connections, so it can take forever to load large images and scroll down to get through sigs with them or a large amount of larger text (like you used in your post - it can fill up a smaller screen very quickly).
Most people have a signature that says something about them, what they like, or want to be reminded of. A lot of authors use their sigs to advertise their stories or threads of particular interest to others, and people w/ pics might link to their AmPics thread.
From what I can gather, the general feeling in most of the forums is that discreet, concise and tasteful sigs and avatars are a good thing; regulars of one or two of our forums are more amenable to louder, longer sigs and more explicit avatars. Whatever you go with, just try to be considerate of others' situations, including how they browse the forums, whether they're at work, in a public place or have kids around, etc.
Per the forum rules (there's a link at the bottom of every page), advertising commercial sites in sigs, posts, etc., is prohibited, and will generally make people suspicious of your motives here.
There are instructions on inserting images into sigs and other common tasks in the FAQs Before Posting sticky at the top of the main How To page, if you need help with that.