When uploading content, you have the option to add tags. The following is an example and explanation of what the different visuals on tags indicate.

Blue Tag - This tag indicates that while the content may or may not already exist, the addition of the blue tag is new.
​Black Tag - This file is already in Content Catalog, and the tag has been added before.
​Minus Sign on Tag - This tag will be removed from the content when it is uploaded.
​Plus Sign on Tag - This action restores the tag, removing the strike through. The tag will remain in place.