The 'x' in 0x stands for hexidecimal
I picked 'z' because:
a) it is not a hex digit
b) it close to x to type
c) it is a mnemonic for zero
d) it stands just enough out
e) it has an hint of symmetry about it -- z is the last character in the alphabet so using it for the lowest number base seems appropriate.
Considering some assemblers have used the dumb '%' percent sign to designate binary, having a consistent form with C's hex literal leaves a little choices:
Using a .. f is retarded because they are hex digits. 'x' is taken. Using I, L, O is dumb because lowercase they blend in.
That leaves: g, h, j, k, m, n, p, q, r, s, t, u, v, w, y , z
0g110101 looks dumb
0h110101 looks dumb, some languages use 'h' for hex
0j110101
0k110101
0m110101 blends in
0n110101 blends in
0p110101
0q110101
0r110101 blends in
0s110101
0t110101 blends in
0u110101 used for unsigned -- not appropiate
0v110101 maybe
0w110101 too verbose
0y110101 maybe
0z110101
So which symbol would you pick??