To the untrained eye, the graffiti tags were just visual noise. They appeared, disappeared, reappeared, ever changing, in what seemed to be a never-ending game of whack-a-mole between tagsters and property owners. For reasons unknown, the tags would keep popping up and disappearing; most people neither noticed nor cared.
For the trained eye, however, these tags told a different story. They told the current preferred locations of illicit trades, mostly in small contraband, easily hidden and easily exchanged between two persons in motion. One week, the tags indicated a particular street corner. Another week, they indicated an abandoned warehouse. Those who could read the signs knew where to go. Those who could not were none the wiser.
In particularly troubled times, the tags indicated a moving target. Being in any one spot for an extended period of time is risky, and necessity being the mother of invention, they invented. It was a difficult tag to make in a hurry, but it could be done: indicating that those interested were to hop on this particular bus at this particular stop at this particular time.
This went on for an untold number of years, out of mind – but not out of sight – of the general population. An anonymous society of secret transactions, unincorporated, but definitely leaving its marks.