Here's her sign...

Hanna has to wear a red ribbon in her tail.  Now I think that is pretty cool to have a fancy doodad decorating your rear, after all my spotted hind end is a beautiful sight.
The DOR says it is actually a warning sign, a flag of shame, a bit of a public service announcement.  You see it seems that when Hanna is in a situation where she is unsure she will kick at other horses to protect herself.  She has even been known to whirl and lunge at them.  The DOR is working with her to develop better social skills.
I happen to think she looks pretty with the ribbon in her tail.  I may take up wearing one in support.
Enjoy your day and don't forget to hug your DOR!