Quote Originally Posted by deker
It similar to English rules:
The dog smells bad. - От собаки нехорошо пахнет - "smells" is a linking verb.
The dog smells badly. - Собака плохо чует носом. - "smells" is an action verb.
Perfect. Thinking about it this way helps a lot. So what I wrote originally was "Your signature is incorrectly." (Almost sounds metaphysical.) Whoops.

Thanks!