I agree that there should be some distinction, horizontal line (similar to what currently separates the attachment area), background shading, frame, or ....
If the sig flows too much into the body text (looking at you, for example), some users might consider it as part of the advice and try to interpret it in context of the discussion. if the sig is too colloquial (even with a separating line, example), it might be read as personal criticism of the OP, even if the sig is meant to be general.