P. Chandra

Adds copyright notice at end of articles in full text RSS feeds, with back links to the blog and original article.
A notice gets attached at the bottom of feed articles like this 
Original Article: Title of Article (linked to permalink) 
Copyright Year. Blog Title (linked). All Rights Reserved
Your Blog title is linked to your blog Url. Your article title is linked to the article permalink.
Blog copyright notices are important as your feed gets freely distributed across the web and is republished without permission by RSS scrappers and autoblogs. After using this plugin, now RSS scrappers will link back to your site, which will suggest to search engines that your blog and article was the original source.

Simple Feed Copyright

Adds copyright notice at end of articles in full text RSS feeds, with back links to the blog and original article.

Hunter Satterwhite

Add custom RSS feeds to your WordPress installation and customize the feeds using theme templates. Each feed contains a unique slug and can use either a custom theme template or if no template is provided then the feed will use WordPress’ default RSS2 template. Easily keep track of what your feeds do by adding a description to them or testing them out clicking the quick link provied in the “existing feeds” table listing.

Custom RSS Feeds by Envintus, LLC

Add custom RSS feeds to your WordPress installation and customize the feeds using theme templates.

Simple Feed Copyright vs Custom RSS Feeds by Envintus, LLC