i dont have one and have never had the need for one, as fetishdj says its not always practical, and i often think holding something is a bit pointless if your hands are restrained that makes it just a little bit awkward lol and if they're not well the chances are that with the type of things we like i would drop it anyway.

IH just checks on me throughout, my breathing,body heat, asks me and tells me to reply in a certain way for yes no etc and he knows me my body and my actions/reactions well to know if things are going well and i trust him totally and have never had cause not to, but i dont use a safeword either.