Why can't I use "RARE" for my clan on COD: BO2?

I used this on BO1 and sometimes it will let me on BO2, I have reported this numerous times.  I think it's crap that I see people with "KKK" as their clan tag, yet I can't use the word RARE?  This makes no sense.  Every time I report this it's temporarily fixed and then it gets taken away again..