Some hits on Google say it means the phone has been accessed by Odin. Others say it's from root, and lastly the bootloader is unlocked. Posting the appropriate S4 section on XDA may provide you with some better clues.
Samsung Galaxy S® 4 MJA Rooted with CF Auto-Root Tutorial
HTC EVO Design 4G™ v4.0.3 Bootloader Unlocked & Rooted with HTC SuperTool v3
If it ain't broke, use a sledge hammer.