Good morning, @PatriciaRacz ...
The short answer is, you can't. This has been a long-standing suggestion here in the Canvas Community, and I would invite you to add your feedback to this Feature Idea: Signature Block. You can also star the idea if you want to rate it. Please note this is not the only way that Instructure gets feedback from users on what we'd like to see implemented in Canvas.
Also, I'll just give a brief explanation on your use of the word "emails" in your question. Canvas does not have e-mail. They have a messaging system through the Canvas Inbox. The Canvas Inbox does not operate exactly like regular e-mail in the fact that you cannot send/receive e-mail messages to/from friends/family via the Canvas Inbox because they are not enrolled in the same course(s) that you are. However, you can set up your Canvas account notification setting to receive e-mail notifications when students/instructors in your classes send you a message via the Canvas Inbox.
I hope this helps to clarify things for you. Sing out if you have any other questions about this...thanks!
