XmGetAtomName(3) on Linux
The text 6b54cab0248c, as Debian 13 (Trixie), Debian 12 (Bookworm), Debian 11 (Bullseye), Debian 10 (Buster), Debian 9 (Stretch), Debian 8 (Jessie) shipped it.
A function that returns the string representation for an atom "XmGetAtomName" "atoms"