In web browsers, default settings typically distinguish hyperlinks by underlining them (and usually changing their color), but both users and websites can change the settings to make some or all hyperlinks appear differently (or even without distinction from normal text).
Unicode has the combining diacritic "combining low line" at U+0332 ◌̲ that results in an underline when run together: u̲n̲d̲e̲r̲l̲i̲n̲e̲.