HDD Led is a simple application that lets you know when your hard drive is reading or writing data. Initially, HDD Led is using the Spotlight icon: it will start twinkling red.
This behavior can be changed via the Preferences window: select Bottom from the Display Position menu and HDD Led will show a small window on the bottom right corner.
To access the HDD Led menu, press the Option and Command keys at the same time and then use your mouse to click on the Spotlight icon or on the HDD Led window.
To uninstall HDD Led make sure you remove it for the Login Items list, delete the HDD Led app, then run the following command in the Terminal: rm ~/Library/Preferences/com.soxcn.hddled.conf