Well, it is very simple. If you are a fan of a YouTuber who is verified then it's very easy to find out. You will see a tick on the side. And if he comments under his own video, you will see his name highlighted in blue as you can see in the above picture.
But if you subscribe to a channel which is no yet verified, you will still see his name highlighted if he comments under any of his own video. I don't know why Mo Vlogs got frighten about this.
Watch from 2:44
How do you know if it's real account if it's not verified?
Well, this one is a bit tricky, there are two ways to find out.
1. If the unverified channel has got custom name which you know for sure then just hover on the picture or name and you will see the URL at the bottom left hand corner (if you are using Firefox) with the custom name. For example: https://www.youtube.com/user/mozartips
2. If the channel doesn't have a custom name then you have to remember the ID of that channel (I highly doubt anyone will remember that) and by hovering on the picture or name you will see the URL at the bottom which will contain the id like Mo Vologs own channel (https://www.youtube.com/channel/UC_hoQDD6zKcIqpIYLsFbBeA/). His account is verified but he doesn't have custom URL.