A lot of "copy the code" features use HTML but HTML is turned off here:

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

I've noticed that some sites (for uploaded pictures, especially) are offering stuff like picture URLs in BBCode, complete with [ IMG] tags. I don't know if your Twitter button could even be implemented that way, though.

I use a dialup connection myself so I already keep signatures turned off most of the time to save on page-loading time. If signatures started acquiring even more features, I'd probably want to do that even more.