The banners and ensigns of the Roman army had idolatrous images upon them, and hence they are called the "abomination of desolation" (q.v.). The principal Roman standard, however, was an eagle. (See Matthew 24:28; Luke 17:37 , where the Jewish nation is compared to a dead body, which the eagles gather together to devour.)
God's setting up or giving a banner (Psalm 20:5; 60:4; Song of Solomon 2:4 ) imports his presence and protection and aid extended to his people.