Ground-fault detection is permitted for grounded systems, but is required for ungrounded systems [NEC Sec. 250.167(A) and (B)].
You must legibly mark your direct-current (DC) system to indicate the grounding type. The marking must be at the DC source or first disconnecting means. The marking must be of sufficient durability to withstand the environment [250.167]. These requirements and the workmanship of Sec. 110.12 exclude the use of hand-written paper signs or similarly unprofession