<kbd> for keyboard keys. Caps Lock, Shift, Esc, C
[tag:tagname] for tags. c,usb
[meta-tag:tagname] for Meta tags. discussion
Use backticks for inline code.
If you see a post where keyboard keys have been expressed using tag syntax, edit it to use
<kbd> notation. Not only is it good style and consistent, it helps users who may not understand what you are talking about or who are using assistive technology.
In certain contexts, there can be true confusion. Did you mean to talk about meta- related questions or about the meta key on the Space Cadet Keyboard or in Emacs?
Don't use something for something it's not intended for unless there is no other way to do it or you have a very good reason.