I will use a double hyphen: -- which Microsoft Word and I think most word processors I've used will auto-replace with an em dash. I will sometimes even type the double hyphen to represent an em dash in places where it doesn't get replaced, like internet comments. I'm kind of surprised more people don't use two hyphens as em dash shorthand, to be honest.
>>brendo+(OP)
IIRC, -- for emdash used to be common on Usenet, which is where I picked it up and still do it. But there's a word for us with usenet experience -- old. (should have been a colon there, but...)