Masked person making a silencing gesture, by placing their forefinger to what presumably are their lips.
<a rel="nofollow" class="external text" href="https://www.flickr.com/photos/39377396@N00">olga.palma</a>
CC BY 2.0
<a rel="nofollow" class="external text" href="https://www.flickr.com/photos/marm0ta/299459344/">shhh</a>