Not depicting pigs, I should say. Look at this example from a calligraphy manual from 1597:
Looks like gibberish or code, but then your eye gets accustomed to the nudge in the middle of each letter, and it becomes readable. Voila, ig-pay alligraphy-cay.
(The above image was copied from the Digital Scriptorium of Columbia University Libraries / UC Berkeley (Google them. It’s an awesome site.) and is © Columbia University. I shouldn’t be using it like this, but look at it. Just look at it.)