Thanks Michelle! I never would have thought of this little issue.
The links and/or words used in your sig line might be sending your emails straight to the recipient’s spam box or not received at all. Link shortners, like bit.ly for instance, could be seen as bad and away your email goes. Even using certain wording like “make money” or “work from home” could trip the trigger.

Take some time to read Michelle’s post, When Good Siggys Go Bad & Get You Tagged as Spam, and then check, not only your sig, but also your domain to be sure you haven’t been blacklisted as a spammer.