hash sign vs hashtag

hash sign

noun

  • The hash or number sign (#). 

hashtag

noun

  • The hash sign itself, when used as part of a hashtag. 

  • A metadata tag, signaled by a preceding hash sign (#), used to label content. 

verb

  • To label (a message) with a hashtag. 

How often have the words hash sign and hashtag occurred in a corpus of books? (source: Google Ngram Viewer )