Filter for removing widget titles that start with !

widget_title_filter.php

<?php

if( !function_exists( 'mpress_remove_widget_titles' ) ) {
    function mpress_remove_widget_titles( $widget_title ) {
        if( substr( $widget_title, 0, 1 ) === '!' ) {
            return;
        }
        return $widget_title;
    }
    add_filter( 'widget_title', 'mpress_remove_widget_titles' );
}