diagonal mark vs slash mark

diagonal mark

noun
  • Synonym of slash as the forward slash ⟨/⟩ and sometimes also its proscribed sense inclusive of the backslash ⟨\⟩. 

slash mark

noun
  • Synonym of slash ⟨/⟩. 

How often have the words diagonal mark and slash mark occurred in a corpus of books? (source: Google Ngram Viewer )