I still don't really understand ambigrams. I've tried.

Ambigrams seem to have been invented independently by a few people around the 1970s. Their first public appearance was in Scott Kim 'Inversions' (1981), followed by a walk-on part in Douglas Hofstadter's 'Metamagical Themas' (1985).

So how do you do them? Well the above is a rotational symmetry one, though you can also do them with various kinds of mirror symmetry, and even translational symmetry sometimes. This entry will concentrate on the rotational symmetry type.

Henry Segerman - Ambigrams