He got a large piece of cardboard, painted a sign begging for the bicycle to be returned, and tied the sign to the letterbox.

他拿了一大块硬纸板，画了一个乞求归还自行车的牌子，然后把牌子系在了信箱上。

youdao

The next day there was a letter in her letterbox.

第二天她的信箱里有封信。

《柯林斯英汉双解大词典》

Peer through the letterbox, and in the gloom you see a calendar pinned to the wall.

通过信箱凝视，在黑暗中你可以看到一个钉在墙上的日历。

youdao

Apps designed for the less elongated displays of iPhones past will still work, but they'll be presented in a less-than-ideal letterbox format.

ENGADGET: Editorial: Engadget on Apple's iPhone 5 event