Hi all, thank you for the feedback and use cases here! I’m on the Product team at HubSpot that is currently building out custom User properties on the User object we released in 2023. We have added a number of default properties (like First/Last name), which you can manage for your users in Settings > Users & teams > Users > Edit User > Profile, and we are now working on building custom properties. We’ll be looking for customers to provide feedback in the coming months, so please email me at jfeeney@hubspot.com if you are interested! I’d be happy to connect with you to learn more about your goals.
To address the initial request from 2017 (wow!), it is currently possible to add the user’s phone number to their email signature using Presets (Professional and Enterprise portals). See this KB doc for more details.