Combining RAC signals and updating UI
I'm familiar with RxSwift, not RAC. :-( That said, I think I can say something constructive about this code...

sig0 and sig1 need more descriptive names.

I would be inclined to break up the combined.subscribeNext function. Something more like:

let buttonEnabled = RACSignal.combineLatest([sig0, sig1])
    .map { obj in 
        let tup = obj as! RACTuple // Wow RAC doesn't return type safe values?
        return (tup.first as! Bool) &amp;&amp; (tup.second as! Bool)
    }

buttonEnabled.subscribeNext { obj in 
    let valid = obj as! Bool
    self.button.enabled = valid 
}


I strongly suspect that there is a function for mapping the buttonEnabled signal directly to the button though, maybe with an Action? You should look into that.