You don't need to sign in to use Skype anymore
 

Unless you have Skype configured to boot-up when you start your computer, starting the program, logging in and connecting to a call can be mildly tedious. It's not anymore -- Microsoft just announced a new 'Guest' mode for Skype that makes user accou...

https://www.engadget.com/2016/11/15/...skype-anymore/