How do you indicate the emphasis that italisizing has when you can't italisize?

for example on Word if I wanted to place emphasis on a word or phrase, i can just italasize it. however on here and on facebook i can only bold things sometimes by puting astrics in front of and at the end of word (ex: "that test went *really* bad). so how do you place emphasis on words here and on facebook and other places where there is no option to actually do so? I know that having words in Caps Lock is supposed to be yelling not emphasizing so i know that's not it.