There is a red seal on the letter.

这封信上有一个红色的钤印。

She placed a red seal on the envelope.

她在信封上盖了一个红色的章子。

The red seal in the first page showed that it had been collected by Yu…

从首页留有的朱印知其曾历经允祥、潘祖荫等人收藏。