My first plugin was Another Author Box. It’s all about front-end knowledge.
So now, I’ve investigated another functions to add signature or similiar contents to rss output. In conclusion, Customize RSS plugin is launched.
This plugin lets you to add links or what ever you want to feed content.
Message position (top or bottom) and default hr element is configurable on settings page.
I think, features can be developable. I can add some other functions like cutting feed off according as word count or showing the custom message depending oncategory/tags/key on forthcoming versions.
Again, it’s on wordpress.org : http://wordpress.org/extend/plugins/customize-rss/
Please do not hesitate to contact me for bugs or suggestions.