Pause notications in OSX whilst in a meeting
When you click on the notification icon in the top bar, you can select "Do not disturb" there by clicking the icon and scrolling up, the setting is hidden above the first notification. You'll see that the icon is greyed out to show the change in state.

As a shortcut you can click on the notification icon in the top bar whilst keeping ⌥ ALT pressed to go into "Do not disturb mode". 

Notifications won't show up now!