Ten is written as two bars, the first coefficient to need no dots at all. Ten is the third day from the end of a trecena, and in the graded reading that living daykeepers give the numbers, the coefficients in the upper part of the range are understood as strong, so a day in the tens carries its sign forcefully.
It is worth being precise about what that means. The reading is comparative rather than categorical: a high number intensifies, a low number is gentler, and the sign supplies the content. That is a modest and coherent system, and it is quite different from the assignment of thirteen distinct named qualities found in modern popular sources.
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.
Planetary, the name given to this coefficient in that literature, comes from Jose Arguelles's Dreamspell of 1987. The atlas holds the Dreamspell as its own system, described in its own right, and keeps it separate from the Tzolk'in it borrows from, because conflating the two is the commonest error made about the Maya calendar.
Sources Maya Hieroglyphic Writing: An IntroductionJ. Eric S. Thompson with Dreamspell: The Journey of Timeship Earth 2013Jose Arguelles