The signature is appended prepended to the top of every email 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 a queue's agents. It is useful if you want to include departmental phone numbers or a link to a knowledgebase. Signatures can have HTML/formatted text in it.
Phone numbers formatted as a hyperlink should use the format tel:999-123-4567. Confluence does not allow "tel:" resources to be included as links in wiki articles.