This place holds following content:
Signing certificates brief
Votre interlocuteur peut adjoindre une signature electronique a son e-Mail vous permettant d'authentifier sa source et de verifier que le contenu n'a pas ete altere.
The sender can attached a signature within the e-Mail which allows you to verify the source is trusted and the content was not tempered with.
What is a public signing key and what's the purpose of it ?
The above key is an OpenPGP public key intended to install in your email client in order to authenticate the sender's emails.
When your sender makes an email, he can sign it with its private key. If you trust the above key and have verified signed emails were received from this person, any further signed communication signed with this key can be trusted to come from this source.