The best replacement for underline is quotation marks.

The best alternatives to underline are rated as following:
★★★★★  quotation marks
★★★★★  italicize
★★★★  italics
★★★★  italicize book titles
★★★★  quotes
★★  italicize books
★★  quotations
★★  quotation
★★  quote book titles
★★  quote plays
★  italicize play titles
★  quote
★  quote poems
★  italicize poems
★  italicize article titles
★  quote movie titles
★  quote books
★  italics book titles
★  underscore
★  italicize articles
★  italicize book title
★  italicize song titles
★  italicize plays
★  quote song titles
  quotation mark
  quote tv shows
  italicize titles
  italicize book titles mla
  italicize poem titles
  quote book title
  italic
  quote movies
  italicize short story

Your alternative for underline is not listed? Suggest!
Speaking about underline, one probably shouldn't forget about html.

Other search terms related to underline and their ratings are:
★★★★★ html
★★★ css
★ different color
You have in mind a companion for underline and it is not yet here? Propose!



Google Trends

Scale is based on the average worldwide traffic of underline in all years. Click on graph for more.
underline
quotation marks
italicize