Dutch coins (and colonial) carry both a mint mark and a privy mark (mint master mark).
The mint mark is usually the Mercury staff for the Royal Dutch Mint at Utrecht. The ancient god of Mercury was patron of the merchant guild and thus had something to do with money.
The privy mark is particular for the mint master in charge at the Utrecht mint, and changes with every newly appointed mint master. In the period that a mint master is released of his function, and a new one is not yet appointed, a * is added to the old privy mark.
During WWII, the Netherlands were occupied, and minting for free overseas territories (or territories expected to be liberated shortly), was done in the US. So these coins carry the P, D, or S mint marks we know from US coins.
The Dutch mint master was not in charge of these mints, so he couldn't exert any authority there. For this reason, a pseudo privy mark was put on the coins. The palm tree was chosen as it represented the tropical colonial areas for which the coins were intended.
The Utrecht mint continued to mint the zinc occupation money for the homeland during WWII. These coins do carry the Mercury staff mint mark, but no privy mark. Allegedly, the mint master refused to relate to the zinc rubbish summoned by the occupier.
A final thing about mint marks: the non-silver 5 cent pieces of the first half of the 20th century carry no mint or privy mark, although they were in fact minted in Utrecht. There was a peculiar reason for this, which I unfortunately have forgotten