Just stumbled upon ambigrams today. Yes, ambigrams. Nice word. What’s that you say? Never heard of them? No worries, neither have I. What’s an ambigram, you ask? Well, according to the Wikipedia entry:
An ambigram, also known as an inversion, is a graphical figure that spells out a word not only in its form as presented, but also in another direction or orientation.
In other words, rotate the image above by 180° and see what happens. There’s plenty more, and they’re quite fascinating.