Copyright marks are also known as "copyright symbols". A nickname for a copyright page in the United States. All published works requiring copyright shall be marked with formal notice on all volumes as a condition of protection.

According to the copyright law of the United States, in order to protect a published work, a mark must be uploaded in the appropriate position of all books of the work, including (I) the word copyright or its abbreviation or its symbol; (II)Year of first publication; The name of the actual copyright owner. The requirement of such a mark as a condition for copyright protection of published works has been accepted by the world copyright convention, the Rome Convention and the phonograph convention, but according to the world copyright convention, the first item of the mark should always be the copyright symbol.

Source: @never_bassic