Adds a small footer to all rss & atom feed posts in WordPress.

mdr_post_rss.php

/********************************************************************************
* Add Footer to WordPress RSS feeds.  Add this snippet to your functions.php
*/

function mdr_postrss($content) {
    if(is_feed()){
        $site_name = get_bloginfo_rss('name');
        $post_title = get_the_title_rss();
        $home_url = home_url('/');
        $post_url = post_permalink();
        $content = $content.'<a href="'.$post_url.'">'.$post_title.'</a> is a post from: 
<a href="'.$home_url.'">'.$site_name.'</a> which is not allowed to be copied on other sites.';
    }
    return $content;
}
add_filter('the_excerpt_rss', 'mdr_postrss');
add_filter('the_content', 'mdr_postrss');