Case wiring! Positive or Negative?

[masterk]

Hi guys, with LED connectors and switch connectors, on the black female part you plug into the board, they have on one side a small arrow on the plastic, does this mean positive or negative??

Cheers.

 

[masterk]

Thanks guys, my main worry is for USB connectors though, the manual rattles on and on about if they are wired up wrong they may damage the USB device.