Definitely not real

I don’t believe in ghosts.  Ghost stories and scary movies scare me (The Sixth Sense freaked me the hell out), but I don’t actually believe in ghosts.  That didn’t stop my heart from leaping into my throat tonight when I saw a pale face lit by a ghostly light in the parking lot near my car.  Half a second later I realized it was a kid looking at a phone, sitting on the curb, wearing a black sweatshirt – his head was totally floating in the dark.  Adrenaline rush: check.  Ghost: nope.

What’s the opposite of “check”?  Do you say “no check”?  Do you say nothing and let the silence tell the person you’re reporting to that you cannot check that item off the list?  Do you get all formal and say “I cannot check this item off the list because it is not complete or does not apply”?  On TV, it’s usually silence, but is there an actual correct answer?  I don’t know how to google that.