Well, don't worry in this post you will find out how you can easily watch that video without signing in.
Go to the URL and replace watch?v= with v/ then hit the enter key. For example from https://www.youtube.com/watch?v=jWBoXdGu4QE to https://www.youtube.com/v/jWBoXdGu4QE
It is like the first one but instead of replacing with v/ replace with embed/. For example from https://www.youtube.com/watch?v=jWBoXdGu4QE to https://www.youtube.com/embed/jWBoXdGu4QE
This one a bit complicated, go to the video and the get the embed code and then make a text file on your desktop open the ext file past the embed code and then save the file as (.html). You might got confused by the last one but don't worry just watch the video below, first tip is about this one.