Understanding Swift 2.2 Selector Syntax - #selector()

I am switching over the syntax of my project toward Swift 2.2 (which xCode helps me do automatically); however, I do not understand the new #selector() syntax.

As an example:

timer = NSTimer.scheduledTimerWithTimeInterval(1.0, target: self, 
             selector: #selector(MyVC.timerCalled(_:)), //new selector syntax!
             userInfo: nil, repeats: true)

This has the selector #selector(MyVC.timerCalled(_:))

What does the _: signify? Can you add other variables into this selector? Say, #MyVC.timerCalled(_:whateverVar).

General info on what is different in this syntax as opposed to the string based implementation from earlier versions of Swift are greatly appreciated.