I found this in a few different places around the 'net - hopefully it's helpful:
Remove Icons for USB Devices from Notification Area
If you have an USB device attached to your system, you will notice an icon in the notification area. When you click this icon, you're given the option to stop your hardware before you unplug it. It's possible that you never unplug this hardware.
- Right-click within the notification area, and then click Properties.
- In the Display Properties dialog box, click the Appearance tab, and then click Advanced.
- On the Taskbar tab, click Customize.
- Select Safely remove hardware, and in the Behavior column, click Always hide.
- You may also hide the icon for a particular USB device by right-clicking its icon on the taskbar, and then clicking Hide Icon.
USB stands for Universal Serial Bus. This is the name for a class of hardware that makes it easy to add peripheral devices (such as a mouse, keyboard, joystick, or digital camera) to your computer. If your mouse, keyboard, game controller, scanner, or other device has a USB connector, you can plug it into a USB port.