Eight is written as a bar and three dots, and one numbered day carrying it has a standing in living Maya practice that no other has. The day 8 B'atz', in the K'iche' reckoning, is when candidates who have completed their training as ajq'ijab' are confirmed, and it recurs every 260 days.
This is the sharpest illustration of why the Tzolk'in is a living calendar rather than an archaeological one. The day is kept, the ceremonies are performed, and the count that fixes them has run without interruption through the colonial period and after it. The atlas describes the observance and does not set out its content, which belongs to the communities that hold it.
Maya numerals are written with a dot for one and a bar for five, and the coefficient of a day is written in exactly that way in the inscriptions, set beside the day sign in its cartouche. The system is positional and includes a sign for zero, which is why the Long Count can be written as a string of places, but within the 260-day count no number above thirteen ever occurs and the notation stays simple.
Galactic, the name attached to this coefficient in modern popular writing, comes from Jose Arguelles's Dreamspell of 1987. Maya organisations in Guatemala have objected publicly to that system being presented as Maya tradition, precisely because it displaces observances such as 8 B'atz' with a parallel count of different design.
Sources Maya Hieroglyphic Writing: An IntroductionJ. Eric S. Thompson with Dreamspell: The Journey of Timeship Earth 2013Jose Arguelles