The history of the hammer is an interesting one. There was a list of party symbols for political parties to choose from. Most of them were absolutely ridiculous eg a Telephone. The hammer was the best of the rest after the PAP and Barisan symbols were taken.
The logic at the time was that most of the electorate were illiterate so a unique symbol was required so they knew which box to tick. It did not matter what the symbol looked like according to the government. (PAP). It was just an graphic identifier.