How does 海报 became "a poster"? I was reading an article in some chinsese newspapare and saw a line


  因为偷了一张题写着政治标语的海报


Why the Hell Ocean + Official Report means "a poster"?

p.s. has it something to do with a postage stamp? You by a stamp, stick it on to an envelope of the letter and send it overseas. And those stamps always have some picture on them like a mini-poster?

P.p.s. Any idea why they called any "theatrical act" - ocean?
Baidu says:

海报这一名称，最早起源于上海。旧时，海报是用于戏剧、电影等演出或球赛等活动的招帖。上海的人通常把职业性的戏剧演出称为“海”，而把从事职业性戏剧的表演称为“下海”。作为剧目演出信息的具有宣传性的招徕顾客性的张贴物，也许是因为这个，人们便把它叫做“海报”。

Which means, if I summarise:
The word originated in Shanghai, where people referred to professional theatrical productions as "海". Hence "海报"