Tag line
noun
(authorship) A sentence part that attributes a piece of written dialogue to its speaker. (e.g. In "Get out of here," he said, "he said" is a dialogue tag.)
“Not every paragraph of dialogue needs to have a dialogue tag attached to it.”
Synonyms: speech tag, tag, tag line
noun
The punch line of a joke.
An advertising slogan.
A pithy quotation habitually appended to a signature in email, newsgroups, etc.