How do I enter keystrokes in a pretty printed form?
For example, the keyboard combination CTRL-SHIFT-D in this answer was pretty printed as
The html tag to produce the any key is
Just to clarify:
Stackexchange sites use an extended version of markdown and allows a certain subset of standard html tags. These tags work in questions, answers and tag wikis. Some stackexchange sites (including the Mathematica one) also allow for LaTeX via MathJax (you can thank the guys at mathoverflow for getting this working first).
The comments only allow a small subset of markdown and AFAIK none of the html tags. See the end of this meta.SO answer.
For examples of some more extreme uses of the allowed markdown, see the meta.SO sandbox