In my circle, most of the time they use the words "yellow" and "red" with the same meanings as traffic signals (slow down and stop). However, I found that I would bottom out before coming up with red - and I think it's because I wear red all the time so it isn't a stop word for me (except those big ones on the corner). So, I use "enough" when I'm at my stopping point -

Sometimes, when I'm being caned, and am in the endorphin space so much that I can't really talk, I simply take the cane away from the Top.

Hope this helps.