We would definitely need this one too
This is keeping us from migrating to Help Desk at the time of writing. It is available in Tickets, why not in Help Desk?
Hi @RBakker86 and thank you for sharing your feedback and outlining your team’s requirements for individual signatures in HubSpot Help Desk.
I can see how important it is for your organization to reflect personalized details.
I’ve noticed a similar idea already present in our Ideas Forum: “Improved customisation of helpdesk email signatures (more personalisation tokens)”.
To contribute, you can upvote the existing idea and share more details about your specific use case in the comments.
I have added my upvote 
Also, as a reminder, there is the workaround from @CTalavera on this thread where they mention you could use snippets in the meanwhile. I understand this is not exactly what you are looking for but I hope it helps in some way.
Have a great day!
Bérangère