> Ctrl+PrintScreen or WindowsKey+PrintScreen (if you want to be fancy).

You actually don't need the Ctrl key. Just PrintScreen will also do the same thing.

WindowsKey + PrintScreen is a nice idea. Problem is, I usually do Alt + PrintScreen. Adding the Windows key doesn't do anything in that case.

SnapChat does notify the sending user if you take a screenshot in any conventional fashion.

Thanks for letting me know. I've never used the service, but it's good to know that they thought of that.