This field is intended to display the owner informations: name, phone or email on the lock screen. Perfect if you have lost or misplaced your device. So I would think that you entered those random letters by mistake.
To enable, disable or change, this go to Settings – My device (or **Sound and display section and then tap Lock screen) – Lock screen – Lock screen widgets.** Then at the bottom press Owner information. Here you can enter any information you want, such as your name or email address.
As a note, if your owner info length is more than 33 characters then your owner info will be displayed as a running text on lock screen.