So what, I am a Joomla Hacker 🙂
I have tried several different ways myself to hide the fact that sites are running Joomla – from hacking in a custom path to the template directory, to using mod_rewrite to simplfy URL references to the /plugins/… directory.
One quick and dirty trick I have found that seems to always bypass these hacks is by appending ?tp=1 onto a URL that I think may be a Joomla site … the parameter tp=1 is a trick that tells Joomla to display its module positions.
So, try it yourself – where else? http://joomla.com