Aside from doing a lot of XPages development, I recently worked on a tool to add mail signatures. The aim was to provide a solution that adds the signatures on a server to avoid to push information to the profile in the users mailfile.
Using a server based solution also makes sure that the signature will be added to any kind of outgoing mails, regardless if it is send from the Notes Client, WebMail or a mobile device.

A signature configuration can be used for an individual user ( or group of users ), a department ( */dev/emea/us ) or fo all users in the company. Within the signature configuration you can use placeholders that are filled at runtime. You can also use a log0, that can be prepended or appended to the signature. You can also use the logo anywhere inside your signature using a {{LOGO}} tag.

This gives you a high grade of flexibility creating the signature.

There can be another signature that is used when sending mails internally.

Signatures are designed using a RichText item; the content is then “translated” to HTML. If you are familiar with HTML/CSS, you can create and style your signature in the HTML item directly.

The tool runs on Windows 2003/2008 32/64bit and Linux ( tested with SLES 11/32Bit )