Concur.....HIJACK
About 2 yrs ago we landed in Hong Kong....and the flaps failed to retract.
We advised the tower who promptly replied "Many thanks, we noticed, you had us worried for a minute there!"
Sometimes I guess you get a flightcrew and controller who remember these "old ways'.
There are many other ways to indicate HIJACK to ATC...... various radio calls/requests etc but in this brave new world in an open forum it probably not the best place to air our little secrets? Who knows who is listening??