It means that the message can be found in the geographical list, number 7638.
The repeaters are used to avoid confusion.

Instead of putting two number 1 flags together, for instance, number 1 is flown with a repeater under it; second repeater repeats number 2, and so on.
PREPARATORY .-- Over hoist.

Prepare to execute subjoined order.
INTERROGATION .-- Alone.

What is that signal?
or "I don't understand--repeat." Above hoist puts signal in interrogative sense.
ANSWERING .-- Flown by ship receiving message indicates that signal is understood.
AFFIRMATIVE .-- Alone.

Yes.