There isn't one, sadly. It has to be a special insert, like a letter with an acute accent. It can be represented by those of us too lazy to copy and paste frequently (me

) by THREE hyphens. Not two, that's an en dash and entirely incorrect for most things. Some word processors automatically convert two hyphens to an em dash but many don't. That's how the whole two hyphen thing became so widespread.
Some places have an en dash as more of one and a half hyphens in size, but since there's no such thing, I round how many I use, lol. You'd be surprised how many grammar books I see are errant in that category. Some only mention the dash in passing like there's only one. That's a pet peeve of mine.
Now I have gotten completely off topic. Apologies, and I'll shut up now.