It's a WD My Book Studio Edition for Mac. I have it plugged in via FW 800, but I just swapped it with USB 2.0 and the gauge didn't change. Have you seen this gauge in the green?
My first thought was heat, but I'm not sure. It's not even hot to the touch. I guess the icon could be on the drive. WD does have an update on their site that makes it a WD logo, but it's for Windows only.