Thanks. I tried Opti Taunt and it wasn't exactly what I was looking for. (Maybe I'll take a closer look it) I believe Curse has; I believe it's called "TankBuddy" but I couldn't get it to work so I chucked it.
My main concern with this is during a 25 man raid when the mob I am tanking; or gaining threat suddenly incapacitates me and a message is sent to the raid warning them.
In most cases when a tank becomes "disabled" it becomes invaluable to let everybody know. Granted Vent works fine, but placing a warning in the chat frame makes it even better.