A UFO is often how our guides show up in dreams when we are first absorbing spirituality and the concept of super intelligent beings watching over us. It's a perfect symbol for that. 

Guides / Angels watch over us throughout our lives and orchestrate the events and people we need to help us achieve our life purpose. They are engaged in your life by prior agreement. If you want their help with other things you have to ask. Respect for free will precludes them from helping unless invited to do so. 

An umbrella shelters you from the rain. In dreams the rain represents life, so being sheltered from it indicates you protect yourself from life. If the umbrella is given to you by someone it tells you who you picked this protective mechanism up from – a man means it is from your father while a woman means it is from your mother.

A dream of an unclean vessel (anything that can hold water, e.g. a cup, glass, bathtub, barrel, etc.) is about your reproductive system. This comes mainly from a religious background where a woman who had a child was considered unclean until purified by the church.

Underground symbolizes your subconscious – something that is below conscious awareness (ground level).

Uniforms are a pun on a uniform or unchanging way of thinking. The dream is asking you to change how you think with regard to the subject matter of the dream.

University indicates spirituality and learning about yourself with a view to improving yourself. See school.

Uphill indicates that you feel life is an uphill struggle. It also means you are on the karmic path.

Dreaming of you upset or someone else upset shows that you are hurting with regard to the subject matter of the dream.

Upstairscan indicate either your spiritual side or your intellect. Look for other symbols that indicate Spirituality in the same dream.

When a dream has a lot of symbols for the heart, the upstairs is often about the intellect. It is very common for dreams to show the cost on your heart because you rationalize all the time (operating from your head).

Walking upstairs can be about activating your spiritual side or your intellect. Again to tell which, you need to look at the other symbols in the same dream.

Urinating eliminates waste that would harm the body. In dreams it symbolizes the need to eliminate an issue from the past or a negative influence in the present. For example, to dream of urinating in the shower while your partner enters and leaves the shower or bathroom is a request to eliminate the negative influence of your partner leaving you. It can also mean you need to (deal with) eliminate the aspects of the relationship that invade your personal space. To urinate in the back of a pickup truck is a request to eliminate the negative influence you picked up from your father (truck) in the past (back of truck).

The United States of America indicates an expansion of consciousness. Much of the Western ‘New Age’ movement has its origins in America. However, America is viewed by many non Americans as a very male oriented society and as such would also indicate being on the karmic path to awareness. This meaning does not hold if you are from the USA.