Created as part of the USB 1.0 spec, the USB icon was drawn to resemble Neptune’s Trident, the mighty Dreizack. (But that doesn’t mean you should go around stabbing people or trying to domesticate dolphins with your flash drive.) 

作為USB 1.0規範的一部分,USB標誌被畫成像是海神強大的三叉戟。(不過這不代表你因該到處去戳別人,或是用隨身碟去調教海豚)

In lieu of the pointed triangles at the tip of the three-pronged spear, the USB Promoters decided to alter the shapes to a triangle, square and circle. This was done to signify all the different peripherals that could be attached using the standard. 

在原來的三個尖端,USB促進團體決定將形狀更改為三角形、方形與圓形。這作法是為了表示所有不同的電腦周邊可以使用此標準來連接。

via The Secret Histories of Those @#$%ing Computer Symbols