Solution to Red Rags

Each image is formed by three national flags. The colors of each flag are modified such that red on the original flag becomes black and all other colors become white. This is clued by the title ("Red"). The left, center, or right third of the flag is shown. Since different flags have different aspect ratios, the relative sizes of the segments vary.

First, the country represented by each flag should be identified.

Drawing lines between the countries in order from left to right gives for each flag, two lines that meet at the center country. Mapping these to semaphore letters (clued by the fact that the images are flags) gives the final answer MENSES, which is confirmed by the title (referencing "on the rag" = having one's period).