Stephanie Leary

This plugin appends the author’s display name to posts and/or pages. There is an option to turn off the display on your own site, so the signature is visible only in feeds and crossposted content.

Post Signature

Appends the post author's display name to posts. Useful for multi-author blogs that are crossposted elsewhere, such as LiveJournal or Facebook.

kei51

This plugin allows you to crosspost your entries to both your wordpress and mixi at the same time. Mixi is one of the most popular SNS sites in Japan.
Once you install this plugin, you will see the option in the edit screen. If you want to publish your post to mixi, you can simply check the option and publish.
You can find the Japanese description at <a href="http://ksnn.com/diary/?page_id=2437" rel="nofollow ugc">here</a>.

publishToMixi

This plugin allows you to crosspost your entries to mixi.

Post Signature vs publishToMixi