I've found these characters in a book called "The Annals of the Cakchiquels", by Daniel G. Brinton. They have a little history, as noted by the tag in the picture. The tz is for a tz sound, and is probably just a glyph variant of that character. The 4 is called a cuatrillo, the reversed three is called the tresillo, and the 4 with a comma is cuatrillo con coma. Are these still in use anywhere? Are they appropriate suspects for Unicode?
In principle they are candidates for Unicode, as it is probable that there is a significant body of historical literature containing them, rather like yogh in Middle English.
Having said that, one would expect a good deal of research to be done before approaching these. How many languages were they used for? What sounds do they represent? How do modern scholars producing critical editions present them? (If they use digit 4, I would consider that to be a fault in the character set or font, and, in my opinion, a Latin letter should be added, because the quatrillo is not a quatro.) Do they appear in casing pairs? On the face of it tz looks like a ligature of t and z.
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Michael Everson * * Everson Typography * * http://www.evertype.com
