Turning Off Notifications While Presenting On Yosemite how can I turn off notifications on Yosemite while presenting or showing the screen to someone?

I know I can set the do not disturb for a time period but I was wondering if there is just an on off switch without having to set a time.
Simplest way is Option (⌥) + Click Notification Centre button; top right corner. It should make the NC dim.  ⟶ 
Open NC then go to Today tab scroll up, it should show Do Not Disturb button, just turn it on.

@Buscar웃 said you can also turn on the keyboard shortcut in System Prefs -&gt; Keyboard -&gt; Shortcuts.