This is an example function on how to add any kind of value to the title. In this case we use the post id

buddyforms_add_id_to_title.php

<?php
add_filter( 'buddyforms_update_form_title', 'buddyforms_add_id_to_subject', 9999 , 3 );

function buddyforms_add_id_to_subject( $default_post_title, $form_slug, $post_id ){

    if($form_slug != 'simple-post-form'){
	    return $default_post_title;
    }

	return $default_post_title . '-' . $post_id;
}