When in a session, I ask the sub to use "time out" to slow things down or to make an adjustment and "red" to stop the proceedings completely.  The latter is rarely used in my experience.  Things are much less formal if we are just experimenting and exploring rather than full on playing "dom/sub" roles and are usually more conversational in nature in those instances.

I prefer to just use yellow to say i am approaching a limit and red to stop.  In many decades of play have never had to say red.  Yellow is helpful to just slow things down.  That way you never have to leave character.  Red would take it out of character.

I think maybe shaking your head no is visible from almost all angles -- if you are gagged and can't say the safe word.

Hi You all!

  I must say, I am really enjoying the convo's on this board!  
( A lot less bitching, and more helpful hints...).

So, I just wanted to drop my helpful hint here:
I took a kink for trauma webinar.  
In it she talked about "creating a safe space",
" the fight-flight activation system",  
and "after care".
  I liked it because it gave me an understanding of the human brain, especially brains that have or are presently experiencing trauma ( and frankly, who isn't? I know I have... ).
As far as setting safe words goes, I got from it that there is an activation - a crescendo- and then an "aftercare" phase to normalize the system again, so you aren't releasing anyone to the wild in a heightened sense. Or, maybe you are? ...

Just, it's nice to have a map. I am a visual learner myself.

I tried to pull it up, I think this is her page. I want to give Angie Gunn full credit.
It's in the links below.

I have the .pdf of her seminar, and I can send it to anyone if they are interested.
I wish I could post the picture illustrating the excitement response.
It was very informative to me, for me - everything "clicked" into place when I saw it!

Well, that's my two cents!
{Insert New Name here}

My dom and I also have a fake safe word ...  its a safe word that she purposely ignores and tells me she doesnt care etc and reminds me she has all the power over my cock and pleasure  .. etc etc.    --------

Believe it or not I have only had a safe word one time in all of my P4P BDSM experiences. It was my first experience at a professional dungeon called "The Chateau" in Los Angeles. The safeword was "mercy" and I ended up using it but only because I thought I had reached the point where I thought enough was enough and she obviously was having too much fun and disagreed. She was spanking me with a ping pong paddle which isn't that severe of an implement unless you do it for a long time in which case the little protrusions or whatever they are in the rubber pad can begin to cause some serious damage.

When I said "mercy" I thought that meant stop immediately and let me go but I was wrong. Instead she asked me if my mother ever stopped when I asked for mercy and I had to admit that she didn't so she asked why should I? When I kept saying "mercy" she told me she was going to throw all of my clothes down the stairs where there were other people present and make me go down naked to get dressed. Eventually she calmed down and let me go.  

I was so traumatized by that experience that the next time I was in L.A. I called the dungeon and asked if she was available.  

Go figure!

If it sounds strange I don't understand it myself.