Signal flags for fleets and merchant convoys

What did lettered signal flags identify before radio call signs, including aboard merchant convoys?

They could designate admirals, squadrons, or convoy divisions so orders reached the intended formation rather than every ship present.

These flags differ from later radio call signs. Letter combinations could identify an admiral or squadron, allowing commands such as breaking off, relaying orders, or concentrating fire to reach only the intended formation. The same logic applied to merchant convoys numbering hundreds of ships, which required senior captains to coordinate divisions. Dutch commercial practice is especially relevant because its merchant fleet operated in formations large and organized enough to resemble a navy.