Hebrew and Aramaic both have a letter called resh.
Perhaps a consonant to represent the "zh" or "jh" sound found in some Chinese and French pronunciations (the G in beige, J in Beijing, CH in Chou En Lai).
Indigo Wallpaper Incense
you would find a illuminated letter on a sign
I think it is because a is basically the greek alpha and alpha is the first letter of the Greek alphabet