Ğ1

Stéphane Laborde says 'Ğ', a Turkish letter that is only used in the Turkish alphabet, has been chosen as a symbol of the unknown, the 'newness of creating economical values that are un-decidable'. That was in reference to the great logician Kurt Gödel for his 'incompleteness theorem', established in 1931, and the GNU project launched by Richard Stallman in 1983 (he is the founder of open-source software, that have been and still are unknown to many, whereas they represent 99% of the internet infrastructure). You can consult https://www.glibre.org/ for more information on this topic

The 1 is used, as it is the first libre currency created.

Duniter

Duniter is literally a UD making machine. The name comes from the French name for UD; Dividende Universel or DU for short. Which explains one reason for the name 'DUniter'. There’s also a reference to the dune pictured in the Duniter logo. A sand dune shows us how sand is renewed with the wind, and that looks the same without being actually the same

Cesium

UD is a part of the money supply created at regular intervals, thus linked to time, time which is measured by… the Cesium atom, which is one of the elements from the periodic table of elements.

Excerpt from Wikipedia : 'The second [...] is defined by taking the fixed numerical value of the caesium frequency, ΔνCs, the unperturbed ground-state hyperfine transition frequency of the caesium 133 atom, to be 9192631770 when expressed in the unit Hz, which is equal to s−1.'
In layman's terms, there's a direct link between the caesium atom frequency and the second.