Exclaimer works great but be aware it has an issue with roaming profiles - redirected appdata folder!

We regularly update our signatures to include information on current promotions, as well as including banners for public holidays such as Easter, and Christmas, which include a holiday greeting and our hours of operation. We also make changes to signatures on a per-department basis, rather than affecting all staff at once. Previously, we would email the new signature to all users in a department and ask them to make the changes themselves, which did not always happen. Using exclaimer allows us to update the signature on behalf of users, at the correct time. It also has the added benefit of being able to add the signature to emails sent from mobiles, which previously we could not do because of the images it contained.

We have benefited from most of these features.
We have different signatures for new emails and replies/forwards
We have different signatures based on user department