Spotted on McLachlan Ave, Rushcutter’s Bay, underneath the railway line is this addition.

Someone, crack the code!

UPDATE (28/8/09):

This one on the left is fading, it’s on Liverpool Street between Womerah Avenue and Victoria Street in Darlinghurst – just across from the Green Park Hotel. The one on the right is newer, it’s on Liverpool Street, near Darlinghurst Road (thanks, Blake).

So now we have:

A is for “azimuth”
C is for “cephlapod”
E is for “entropy”
K is for “kibosh”
M is for “modulate”
N is for “nebulous”
T is for “thought bubble”
Y is for “yesterday”
Z is for “zipper”

Riddle or just randomly chalked letter clarifications?