Maybe this one isn't as not-known as I think (I've only ever seen it used on a handful of old posts), but, if you post while in ;wap2 mode (or ;imode,
<snip>
you can get PHP code-coloring with [code][/code] tags, too:
<snip>
BTW, here's a (I think) complete list of the 59 BBCode tags that the parser recognizes (it's an alphabetical arrangement of the 57 tag names that I found within SMF 1.1.19's parse_bbc function, plus the [btc] tag which came from theymos, and the [nbsp] tag which came from me):
<snip>

Funny how I didn't actually know before then that there was a specific PHP tag <snip>
php code.
<snip>PHP coder

<snip>I imagine (like php) it is to syntactically color this language