I have sometimes been asked and answered this question, but I think it may be something many would have use of knowing (and some don't dare ask):
If you want to u̲n̲d̲e̲r̲l̲i̲n̲e̲ or o̶v̶e̶r̶s̶t̶r̶i̶k̶e̶ words in systems that only accept text input (like here on GNUsocial/Mastodon), then those are very handily available as unicode-character translation websites.
Underline: https://fsymbols.com/generators/underline/
Overstrike: https://fsymbols.com/generators/strikethrough/

Just... be aware that some people may use clients that can't handle it (but should in 2018) so there COULD be misunderstandings as a result.
Probably not, but... there you go.