I should explain that I did not invent the concept of ambigrams — to the best of my knowledge, they were invented in about 1962 by my friend Peter Jones, when we were both undergraduates at Stanford University. Peter and I both did a few ambigrams around the time he invented the concept, but we did not carry the art form very far. The idea was then independently reinvented in the mid-1970s by Scott Kim, who was at that time a math/music major at Stanford University, and John Langdon, at that time a young graphic designer in (I believe) Philadelphia. It was Scott who, when we first met in 1975, revealed to me how interesting the art form was, and how much potential there lay lurking hidden in it. (I did not find out about John's work until many years later, nor did Scott. I think John is today the world's most publicly visible ambigrammist, since he did the ambigrams in Dan Brown's hugely popular book Angels and Demons, and in fact the hero of that book is named “Langdon”!). Inspired by Scott's wondrous creations, I took up the art of ambigrams very intensely, and since then have done thousands of them, as have both Scott and John (and perhaps a few other people). All three of us have published books of our ambigrammatical art, although mine, regrettably, has appeared only in Italian. (John's is called Wordplay and Scott's is called Inversions, while mine is called Ambigrammi.) In late 1983 or early 1984, since there really wasn't any good word for this art form, I coined the word “ambigram,” and that seems to have been the term that people have gravitated to, over the years since then.
There is a small community of ambigrammists around the globe. Of course, anyone at all can do an ambigram to some extent — the real question is, how good is it? This boils down, in my opinion, to a few questions, as follows. How legible is it? How graceful is it? How well can the person resolve a large number of highly diverse challenges? The criteria that, by my lights, are crucial in this art form are: (1) rapid, easy legibility by a random viewer, and (2) grace and unforcedness. If these two criteria are not respected, then any piece of calligraphic junk (one could call it a piece of “cacography”) could be called an “ambigram.” Unfortunately (or fortunately), of the many self-proclaimed ambigrammists in the world, there are very few who in truth meet these key criteria in most of their output.