You might know the mnemonic for $\pi$ in the title or even this more elaborated one:
Sir, I bear a rhyme excelling
In mystic force, and magic spelling
Celestial sprites elucidate
All my own striving can't relate
Or locate they who can cogitate
And so finally terminate.
Are there any for other than $\pi$? Feel free to create your own! Here's my try for $\gamma$:
"0 Euler Leonhard" $\to 0,58$
Choose your favorite language and feel free to post a riddle...