According to Wikipedia, it's an awareness ribbon for several things:
- Sickle Cell Disease black ribbon with spiraling red crescents intended to represent sickle cells
- terrorist attacks in Turkey; a sign of mourning for those lost in the terrorist attacks
- Wiccan/Pagan rights and awareness
- 9/11
- mourning and remembrance of the Virginia Tech massacre
- mourning of Hong Kong victims in 2010 Manila hostage crisis
- melanoma awareness
- narcolepsy
A black ribbon is a symbol of remembrance or mourning. Wearing or displaying a black ribbon has been used for POW/MIA remembrance, mourning tragedies or as a political statement. ~Wikipedia