haha I was the OP of the user name thread. (Is OP used on this site?)
Text surrounded by asterisks (*) is italicized.
Text surrounded by plus signs (+) is bolded.
Text surrounded by vertical bars (|) is quoted. If you double-click a paragraph, it will be quoted.
Text surrounded by tildes (~) is blocked out.
Symbols such as *, +, |, and ~ can be used literally by placed a \ in front of the text.
A user's name surrounded by at signs (@) links to their profile, and the user is notified that you mentioned them.
A word surrounded by hash signs (#) becomes a tag and links to posts with that tag.
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Yeah. Pretty much any abbreviation you see on Reddit (OP, IMO, YMMV, etc.) will be fairly well-understood here.