○△た in the flag symbolizes each social standing of the group.
○○○○○○ symbolize 6 samurais.
△ implies Kikuchiyo himself, who is not a samurai but a would-be samurai.
He is actually a peasant. In Japanese culture, we place △ between ○ and ×.
た is the first letter of たんぼ（田んぼ）, which symbolizes peasants (in the village).