The word "هلال" (Hilaal: ha, lam, alif, lam) and "الله" (Allaah: alif, lam, lam, ha) are formed using the same letters and abjad count both mounts to 66.
The Ottoman, not wanting the name of Allaah (jalla jalaaluhu) to be possibly disrespected by kuffar (in the case of defeat, flag burning...