Post score is a behaviour that works in the background. It take whatever attribute you assign to it and puts it on the GameCenter leaderboards, providing you have set it all up correctly. If you want the button to post confirmation or show kind of recognition to being hit, then you do that in the rule of your button actor.
i.e. When touch is pressed Change Image to darker image Post Score Play sound
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i.e. When touch is pressed
Change Image to darker image
Post Score
Play sound