Three is written as three dots, and the third day of a trecena is the last that can be written in dots alone before the count reaches four. In practice all four of the first coefficients are written with dots and the fifth introduces the bar, so the visual character of a numbered day changes as the trecena advances.
The coefficient is not a property of the day sign it accompanies. Any of the twenty signs can carry any of the thirteen numbers, and over a full 260-day round each does so exactly once, which means a sign appears with the number three once in every round and a specific numbered sign such as 3 Akbal recurs only once in 260 days.
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.
Electric, the name attached to this coefficient in modern popular writing, originates with Jose Arguelles's Dreamspell of 1987. It is not a Maya term and does not appear in the Classic inscriptions, the codices, the colonial Yucatec sources or the practice of present-day daykeepers, who use the numeral.
Sources Maya Hieroglyphic Writing: An IntroductionJ. Eric S. Thompson with Dreamspell: The Journey of Timeship Earth 2013Jose Arguelles