Here's a guide on the various codes that can be seen when you monitor a link:
Not Linking -
There is no link from this page to the domain you are monitoring.
Follow (#) -
This is how many links are marked as active follow links. This can include image links as well!
No Follow -
This is how many links are marked as no follow.
Error 301 -
This means that there is a page re-direct when someone clicks on this link.
Error 404 -
This means the page cannot be found, thus there is no active link. The typical trigger for Error 404 is when a website or its content has been removed or moved to another URL.
200 -
This means that your link is active.
While in Link Monitoring, you can find these definitions by hovering over "Linking URL Status."