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
0m110101 blends in
0n110101 blends in
0r110101 blends in
0t110101 blends in
0u110101 used for unsigned -- not appropiate
0w110101 too verbose
So which symbol would you pick??