Yeah - I've done a bunch of these, not to mention Mod Month and Meetup posters. Not sure this one has shown up lately, but here you go - it's a vent code identification cheat-sheet, but it needs to be updated. The original 1952 vent had no markings on it at all.
And here's one of the more recent vent-code posters that kind of matches up to the one above:
This one was early, and kind of random, and is also missing the original 1952 vent. I have that update somewhere...
And one that someone here turned into wrapping paper:
I'll keep all these in the following Flickr album so you can download/print to your heart's content:
https://flickr.com/photos/32306142@N07/albums/72157712666285736