Seeing an army's flag in your dream signifies that you are witnessing a symbol of a virtuous, pious, or righteous person. It indicates the presence of a leader in your life who may serve as your inspiration and guide. If the flag is red, it represents strength, courage, and leadership. This could mean that someone is about to enter your life who can offer you a new perspective.
From Imam Muhammad Ibn Seerin's Dictionary of Dreams According to Islamic Inner Traditions â entry "Army's flag" (page 20).
In a dream, the flag of an army represents a pious man, a scholar, a religious doctor, a spiritual leader, an ascetic, or a rich and a generous person who is an example to others. A red flag in a dream means war, while a yellow flag means a plague. A green flag in a dream means a blessed journey, while a white flag means rain. A black flag in a dream means drought and doubt, or it could mean a rainstorm. Sighting the flag of an army in a dream means finding one's way or finding guidance. For a woman, seeing a flag in her dream means getting married. (Also see Banner; Colors; Flag)
Note: Islamic dream interpretation depends on the dreamer's circumstances and state. This is a general guide drawn directly from the source book.