Matoi flag is drawn on the lid, flags that were used to announce a fire during the Edo period in Japan (17th-19th centuries). The flag would be waved in the air on rooftops near the burning building, to notify the fire department of the location of the fire.
See another cap with this flag
Translation of the text on the cover: 消火栓 - Fire hydrant 黒部市 - Kurobe City