Typically black on a yellow background, does a small dot surrounded by three slices of pizza mean anything to you? Recognisable around the world, this symbol informs us of radioactive danger (or exposure to ionising radiation, to be more specific). The symbol is also known as the “radioactive clover”, because electricians identified three-phase current (a system that helps limit electricity loss, consisting of three sinusoidal currents at the same frequency and same amplitude, which are out-of-phase with one another by a third of a turn) using a three-leaf clover. The clover then reappeared in 1972 as the international symbol for radioactivity.