'An acronym is an initial abbreviation that can be pronounced as a word, such as NASA or WASP. This term is also used to refer to a series of initials pronounced individually, such as FBI or TGIF, but the technical term is initialism.
Because acronyms like NASA are pronounced as words (“na-suh,” in this case), there’s no need to precede them with the definite article: You wouldn’t write “Budget cutbacks hit the NASA hard.” (Though the is essential if NASA is used as an adjective, as in “Budget cutbacks hit the NASA project hard.”)
But initialisms require THE: “The FBI announced his capture several hours later" That’s because the term is pronounced letter by letter: “eff-bee-eye.”
So what about RBS, HSBC, BT, BP. They're all pronounced letter by letter and none of those are ever preceded by 'the'. So are they acronyms or initialisms?
http://www.dailywritingtips.com/initialisms-and-acronyms/