Question

Ba-3 what does a red flag with a diagonal white stripe mean?

Answer 1

It is a divers flag. The divers flag is also referred to as the scuba flag. It is used as an indicator when a diver is below the water. There are two types of divers flag. It is used to signal that I have a diver down hence keep clear and sail at slow speed. The north American flag is red with a diagonal white stripe. while the international flag contains white and blue color (Also known as signal flag alpha).

Answer 2

A red flag with white diagonal stripe is a Diver flag.
(a sample flag is shown below)

Dive flaga are used in purpose to show that divers are work in progress. It means that the diver is working near the surface of the water.

There are other types of flag as well which have other purpose.