A Vaishnavism tradition of vertical forehead mark. The three lines signify three Vedas, the A+U+M of Om symbol, Maya + Brahman + Atman, three Guna or qualities (Sattva, Rajas, Tamas), etc
<a rel="nofollow" class="external text" href="https://www.flickr.com/people/32856635@N00">Jean-Marie Hullot</a> from France
CC BY-SA 2.0
<a rel="nofollow" class="external text" href="https://www.flickr.com/photos/jmhullot/2318802427/">Haircut of the Day (Pashupatinath, Nepal)</a>