Can users edit the email signature?
You can configure if you want users to be able to make changes to the email signature in the Outlook Options dialog. By default users cannot make changes to their email signature. If you allow changes, then users can make changes, and any such changes will only be overwritten if you change the Email Signature Manager template. See the Install Read Only option in the user's guide for more information.
Users can edit the email signature when composing an individual email. If they do so the email signature will revert to the Email Signature Manager version on the next email they compose. It is not currently technically possible to lock the signature Emails are saved in Sent Items including the signature, and any changes the user may have made to the signature.