WordPress – Add Post Type Labels to Post Titles

function add_post_type_label_to_title($title, $id = null) {
 
    // The html before the insert after title
    $html_first         = '<span class="example-post-type-label">';
 
    // Title after defaults to false
    $title_after        = false;
 
    // The html after the insert after title
    $html_after         = '</span>';
 
    // Allowed post types
    $allowed_post_types = array(
        'post',
        'quickie'
    );
 
    // Make sure we're filtering title in the loop
    // Note: This will also filter singular titles
    if(in_the_loop()) {
        $post_type          = get_post_type();
 
        // Uncomment if you don't want the label to appear on singular templates
        // if(!is_singular($post_type) && !is_single()) {
            if(in_array($post_type, $allowed_post_types)) {
                $post_type_obj  = get_post_type_object($post_type);
                $title_after    = $post_type_obj->labels->singular_name;
            }
        // }
 
    }
 
    // If we have a post type
    if($title_after) {
        return $title . $html_first . $title_after . $html_after;
    }
 
    return $title;
 
}
 
add_filter( 'the_title', 'add_post_type_label_to_title', 10, 2 );

// This is just some example styling.
// Do something more fancy than this
add_action('wp_head', 'add_post_type_label_eg_css');
function add_post_type_label_eg_css() {
    $output="<style>
    .example-post-type-label {
        background-color : #f1f1f1;
        font-weight:bold;
        font-size:13px;
        padding:5px;
        margin-left:15px;
        display:inline-block;
    }
    </style>";
    echo $output;
}