If you are using Office 365 and have deployed the Signitic Add-in, you have the ability to set up signature delegations.
Delegation allows you to display a signature from a user other than the logged in user. It also allows you to have access to the signatures of your shared mailboxes on Outlook Windows.
1️⃣ Access the Users menu
To activate the delegation of a user, go to the profile of the user whose signature you wish to delegate and click on Modify.
2️⃣ Add a delegation
Go to the Settings tab, then simply type in the emails of the users who will have access to this signature.
Save and you're done!
On the Add-in side, thanks to the delegation, the right signature will be displayed directly when you write from the shared mailbox as well as when you open the Add-in.