If you hover over the icon you may get some help text.
The most common one refers to a situation where the Auditing was stopped and started again.
Even when the auditing is stopped and started straight away you will get this. It is very annoying and my guess is that it is a bug. I believe where the 'New Value' shows this icon you can get the new value from the record itself.
Hope this helps.
Proposed as answer byTroy AdamsFriday, March 14, 2014 4:20 AM