The sign already conveys visually what it warns against, but still if it helps:

• 周りのこと考えて！　"Think about the people around you!" (The sign is being more commanding. It's not saying "please")

• 大きな声で楽しそうなフクロテナガザル…　でも、車内では静かにしてね　The Siamangs are loud and happy. But, they should/need to be quiet on the train

• ホゥ　loud monkey noise

• あらあら　oh dear/oh my

• 車内では周囲への気づかいを　Take consideration of/toward your surroundings on the train