What are the three waves on the stamp?

Stamp According to the relevant information of the inquiry stamp, the three waves on the stamp are postmarks. In order to make the stamps unusable, the post office will cancel them. The most common ones are stamps. Postmark is a kind of postmark stamped by the post office on the actually sent mail package, including ordinary postmark, commemorative postmark, publicity postmark and so on. Is a reflection of history. Collecting postmarks has become an important part of stamp collecting. Now there are also new types such as electronic postmark.