1. （通常指在抗议或集会中用两根竿子撑开的）横幅，标语
    A banner is a long strip of cloth with something written on it. Banners are usually attached to two poles and carried during a protest or rally.

banner的翻译

    e.g. ...a large crowd of students carrying banners denouncing the government...
           一大群高举谴责政府的条幅的学生
    e.g. A big banner was draped across one of the streets saying, 'Idaho Falls Says NO to Drugs.'
           一条写有“爱达荷福尔斯市拒绝毒品”的大横幅悬跨其中一条街道。

2. 在…的旗帜下；为了…的事业（或信仰）
    If someone does something under the banner of a particular cause, idea, or belief, they do it saying that they support that cause, idea, or belief.

    e.g. All countries march as one nation under the banner of friendship.
           所有国家在友谊的旗帜下团结一致，共同前进。
    e.g. Under the banner of education, we herd our children from ballet to basketball and back again.
           打着教育的旗号，我们赶鸭子上架似的让孩子从芭蕾到篮球，不停地学这个学那个。