Ejnar Hertzsprung’s two-letter abbreviations for the constellations
Reproduced here is Ejnar Hertzsprung’s list of two-letter constellation abbreviations, published in 1922 in Annalen van de Sterrewacht te Leiden vol. XIV, part 1, p. 22. Hertzsprung used primes and even double primes to distinguish between constellations with otherwise identical two-letter symbols. Despite popular misconception, Hertzsprung was not party to the table of three-letter abbreviations adopted by the IAU in 1922. His opinion of those abbreviations can be read here.