The days signs meaning in Florentine Codex Book 4 is based on the 260 day calendar --I’ll attempt at making it easy to understand. The day counts don’t always go exactly the Gregorian dates as the title may indicate since it's based on a 260 day calendar along with the 5 unnamed days (which many websites forget to add on their interpretation of the calendar), but the days are reused and their meaning is still valid. These days can be used for future references when the same day sign appears again in the calendar, which the day signs will be noted in the title.
Lets start with the year; the year is Ce Calli, 1 house.
March 12th is the start of the calendar starting with Ce Cipactli (1 alligator). This day is a good sign for those who were born in it.
If a nobleman was born on these days, it was believed that he can become ruler, prosperous or wealthy.
If a common man was born on these days, he would be a great warrior.
If a woman was born on these days, she would be wealthy and prosperous.
There is a catch to this; if the person became malicious acting on evil intentions, it would lead them to an inevitable unhappiness, ultimately leaving them to suffer in loneliness.
Usually the child will be given the name Cipac or a name of one of their grandparents.
Guardians for this day are Oxomoco & Cipactonal.
The days following Ce Cipactli is Ome Ehecatl (2 Wind), Ei Calli (3 House), Naui Cuetzpalin (4 Lizard), Macuil Coatl (5 Serpent), Chicuacen Miquiztli (6 Death), Chicome Mazatl (7 Deer), Chicuei Tochtli (8 Rabbit), Chiconaui Atl (9 Water), Matlactli Itzcuintli (10 Dog), Matlactli Ce Ozomatli(11 Monkey), Matlactli Ome Malinalli (12 Grass), Matlactli Ei Acatl (13 Reed). These days are good as well.
Jia Escobedo helped with editing.