I did a little research, and here's what I came up with:
Some purple awareness bracelets are for:
-Harry Potter and the Half-Blood Prince release reminder
-Fathers' rights and Justice in family law
-Erase Hate Campaign - Matthew Shepard Foundation
-CARE/Borders (global poverty/literacy)
-National Kidney Federation (kidney disease research)
-Pancreatic Cancer awareness
-Purple Paws Foundation
-Relay For Life cancer foundation
Sorry that that doesn't really narrow it down.
Maybe one of them will make sense to you based on where you received it.
For more "awareness color" choices, you can check out this site: http://en.wikipedia.org/wiki/Wristband