

Incognito Mode offers similar functionality to not signing in to YouTube in first place. Select Paid Memberships from the menu, tap on the menu again and there you have the sign out option. Update: Apparently, there is still a way but it is quite hidden. You can exit the mode at any time by tapping on the incognito icon that is displayed instead of the profile icon and selecting "turn off incognito".

Incognito Mode is turned off automatically after a period of inactivity. When you open search, YouTube reminds you that the search history is paused while the mode is active. Other parts of the app may remind you that activity is not recorded. Some functions on YouTube, subscriptions, for instance, become unavailable while you are in incognito mode.
