Apparently, bankrupt, discount Canadian airlne JetsGo is still flying, if only in theory (emphasis added):
THE American military have been operating flights across Europe using a call sign assigned to a civilian airline that they have no legal right to use.
Not only is the call sign bogus — according to the International Civil Aviation Organisation (ICAO) — so, it appears, are some of the aircraft details the Americans have filed with the air traffic control authorities.
In at least one case, a plane identified with the CIA practice of “extraordinary rendition” — transporting terrorist suspects — left a US air base just after the arrival of an aircraft using the bogus call sign.
The call sign Juliet Golf Oscar (JGO) followed by a flight number belongs, says the ICAO, to a now bankrupt Canadian low-cost airline called Jetsgo of Montreal.
Sure, it's tacky but, come on -- JetsGo is bankrupt. It's not like they need that call sign or anything, right?