Marks of wartime

I have walked in the Gardens so many times and yet it was only today that I stopped to read the sign at the foot of these steps.
the sign reads
These steps and bricks were made by prisoners of war (PoWs) during the Japanese occupation of Singapore (1942-1945). As a sign of defiance, the PoWs imprinted arrows on most of the bricks to indicate that they “detained by the authorities”. In August 1995 at the 50th anniversary of the cessation of hostilities, eight former Australian prisoners of war (PoWs) visited the Gardens in order to observe their wartime workmanship and gleefully recounted that memory.