Soli

This plugin allows you to append a signature after every post. Some variables can be used, such as %post_title%, %post_link%, %bloginfo_name%, %bloginfo_url%, and so on. It supports multiuser.

WP Post Signature

Works great for me

This plugin allows you to append a signature after every post. Some variables can be used.

Abinav Thakuri

The WordPress Signature plugin allows wordpress users to have signatures below every post.This is almost similar to forum signatures where you can have a default signature on every post you make.The plugin is still being developed and the signature need html formating to appear properly.This means tags like <code> </code> before the signature and anchor tags for links.This will be made easier in future versions.

WordPress Signature

The Wordpress Signature plugin allows wordpress users to have signatures below every post.

WP Post Signature vs WordPress Signature