There is only one way to create sigs that include your own model.
-Your model needs to be in the view (not only the eyes)
-Your model needs to be skinned (model only looks crappy)
-Your model needs to be posed (rendered whatever you wanna call it, but a guy standing with his legs spread and arms wide, just looks boring, but a guy (for example) standing in a cool stance with a sword or something looks way cooler)
After that you need to make a nice bg and blend the model in it, otherwise...it will just look stupid