The screen capture in question was indeed from a Trireme.
The Cicilian pirates flew the skull and crossbones (probably a different variation and not on a black background) and other death symbols. Their primary ship was the trireme, so that makes sense. They were the pirates who took Julius Ceasar captive and held him for ransom. When the ransom was paid, he promised not to harm his captors. Later, he came back and defeated them, crucifying the survivors. Nice guy!
