Right! If you want it to denote an action, you need to include the verb: "TURN ON" would be entirely clear. It's even clear if you sometimes DO want to show state / not a button "IS ON" is also perfectly clear. There's only a few that might he confused when the verb is shown, like "INCREASE," although I would have to work a little to imagine the UI where it's not clear whether the button is showing the verb or noun.