My husband's and my safety word (although we have never had to use it because we maintain constant communication) is "Oklahoma."

As far as the power of D/s in our relationship, our BDSM lifestyle is very casual, and we don't live it in everyday life at all- it is pretty much just a sexual thing. Scenes, punishments, and BDSM erotica are administered/participated in at whim, when the mood strikes us. As for who holds the power, we are switches, so we pretty much have an equal balance of power.