Poseidon was the god of the sea, earthquakes, floods, droughts and horses.  He also had his own look and symbol, as the article, "Poseidon," elaborates, "He was depicted as a mature man with a sturdy build and dark beard holding a trident (a three-pronged fisherman's spear)," (Atsma). Poseidon's trident was fashioned by the three Cyclopes,  just like his brothers'  physical  symbols.

"Greek God Poseidon"