It’s actually possible to print text upside down using a simple CSS property and works cross-browser today. The property to use is “text-gravity” with a value of “inverse”.

<span style="text-gravity:inverse">
write upside down text
</span>

… and this is the result:
ʇxǝʇ uʍop ǝpısdn ǝʇıɹʍ

I’m really surprised to learn that so few people know about this property, and I recommend you to continue reading the W3C specification of text-gravity.

Update: Sorry, I lied 🙂 The above is done with a UTF-8 character generator (see the link the the “specification” above). Amazingly, you can find that most characters have their upside down equivalent somewhere else in the huge Unicode alphabet. Neat trick 🙂 Here’s another site that does the same thing.