To see an X in your dream signify something that is forbidden. You are being prevented to do something.
To dream of a treasure map marked by a big X indicates that your goals are in sight and you will soon be greatly rewarded.
To dream that you are being x-rayed denotes that you are being deceived by a person or situation. You need to look beneath the surface of the person or situation. On the other hand, the dream means that you are working through a problem or issue that has been troubling you.
To dream that you have x-ray vision suggests that you need to look pass the surface and focus on what is inside. Perhaps the dream is trying to tell you that looks aren't' everything.
To see or play a xylophone in your dream indicates concerns for the environment. You need to be more environmentally conscious. Alternatively, the dream represents your ambition and your drive. It also provides motivation and inspirational insight into the future.