Which ensign provided a symbol of authority on revenue cutters when neither officers nor crew had uniforms?

The correct choice is the Revenue Cutter Ensign, which served as a significant symbol of authority for revenue cutters during a time when neither officers nor crew members wore uniforms. This ensign was specifically designated for use by the Revenue Cutter Service and later became incorporated into the United States Coast Guard. The Revenue Cutter Ensign played a crucial role in visually representing the authority of the cutter while conducting missions related to customs enforcement, maritime safety, and law enforcement on the high seas and waterways.

The other options refer to different types of ensigns that do not specifically apply to the historical context of revenue cutters. The Merchant Ensign generally represents commercial shipping and does not convey the same authority as the Revenue Cutter Ensign. Similarly, the Coast Guard Ensign and Coast Guard Ensis are contemporary terms that represent the modern Coast Guard but do not encompass the specific historical significance of the ensign used by revenue cutters in earlier times. The Revenue Cutter Ensign is clearly distinguished as a unique emblem of authority within that specific naval context.