OK. I'mma be clear, here. I think this is sum bullshit, and I don't do it in my relationships, BUT people do for their own reasons, and I'm going to explore this, so you have examples of how "No" can be used that is not actually "No."

(Feels very "Depends on what your definition of "is" is, to me, but you do you...)

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NO! Means Yes! 

In Polish, "No" spelled and pronounced exactly that way is an affirmative response. It's used less often as a direct response:

"Will you kink with me?"
"No." <--- Not really the right grammar, more likely to use "Tak," (yes), or "Nie" (no). 

"I love to kink!"
"No," (yeah) or "No to dobra," (yeah, it's good).

Polish speakers use "no" in conversation to show they are listening, as English speakers might use "Yeah," "Sure," "Uh huh," or "Go on..."

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NO! Means "I'm being playful!"

Some people like to play the brat in their relationships (whether power exchange or not). In those situations, "No" might mean "Make me," or "Chase me through the house growling, while I giggle until you catch me and have your naughty, naughty way with me."

In a case like this, I would suggest that you have a word that really doesn't fit into most situations naturally that can be used to mean "No, 100%, absolutely," so if there is confusion or an actual hard "no" needs to be uttered, that word can stand in it's place. 

For example:

Red
Snicklefritz
Asparagus
IMeanNO
Meatloaf (I'll do anything for love, but I won't do that.)

When something like this is negotiated and put into place in a relationship or a scene, it's often called a safeword. 

All of these are safewords I've encountered in my time in kink.