buffer-charset.el lists charsets used in a buffer and can highlight characters from a particular charset. Get it from the emacs-devel post
buffer-charset.el after downloading). The message is http://lists.gnu.org/archive/html/emacs-devel/2002-07/msg00672.html
Listing charsets used is good for finding out what you’ve cut and pasted, especially when emacs is arguing with you about a “safe coding system”. It’s also good to see if there actually are any characters from a
coding cookie, or if it’s in fact just ASCII.