The signature is appended to every response sent by someone in your department. Unfortunately, you cannot have a signature based on the user, only for the department. If you reply to tickets with email and you have a signature in your personal email, that would get captured by ServiceNow and sent to the ticket originator so it may not be necessary to have it twice. The downside is when you respond in the web interface, you wouldn’t have signature information available. In some cases it is better to reply in the web interface, while other times it’s easier to just respond using email. This can have HTML/formatted text in it.
Anything phone number that appears to be formatted as a hyperlink should be a hyperlink using the link format tel:999-123-4567. Confluence does not appear to allow "tel:" resources to be included as links within wiki articles.