To see the letter "U" in your dream is a pun on "you" and how you act and behave in your waking life.
Consider what were you doing in the dream for understanding it better
The dream also signifies a restart. You need to go back and redo something all over again.
Letter U is the 21st letter of the alphabet and 21 in numerology represents conflict with confrontation.
You are having a problem changing or standing up to something.
Seeing letter U in dream also suggests that you need to take U turn in what you are doing.
It also means that you are not liking your current situation how it is turning out.