Letter S appearing in Header

In your Header code, there is a stray ‘S’, which then appears at the left-side of the Header.

<nav id="site-navigation" class="main-navigation container" role="navigation" aria-label="<?php esc_attr_e( 'Primary Menu', 'thesimplest' ); ?>">
				            <?php
				            wp_nav_menu( array(
					            'theme_location' => 'primary',
					            'menu_class'     => 'primary-menu',
					            'fallback_cb'    =>  false
				            ) );
				            ?>S
                        </nav><!-- .main-navigation -->

It’s located at about line 81, right after the closing php bracket.