Why XBT using instead of BTC sometimes? What is XBT?
A lof of people did see screen shot of JPMorgan's buying Bitcoin. But there was "XBT" in the picture.
Currency symbols must be uniq and same for whole finance market. There is an Organization for this: ISO: International Standards Organization.
// yes that "ISO-9001 license..." we hear a lot.
ISO has set the letters for the currency symbol of each country, for example: TRY, USD, EUR, GBP.
However, according to ISO standards, the symbol for assets that Copper, Gold, and so forth do not depend on an individual country begins with X. Exp: XAU, XAG
So Bitcoin, which is not affiliated to any country, has to start with "X".
http://money.cnn.com/quote/quote.html?symb=XBT
In summary, do not be surprised if you see the XBT symbol instead of BTC for the Bitcoin follower in companies that do business like the Capital Markets Board and their corresponding regulatory license. That's Bitcoin.
Perhaps there may be a difference; CNN; It's getting the average of Bitfinex and BitTrex. A company in another country is getting the average of Polonix and BTC-e.