Imperial standard; brocade banner
Historical term for the banner used by the Imperial court, especially during the Boshin War, to legitimize a military force as the Imperial army.
In the Boshin War, the side that raised the Imperial standard was considered the Imperial army.
worthy cause; noble banner
Idiomatic extension: used to describe a cause or principle invoked to justify an action, often with a nuance of self-righteousness or pretext. Common in phrases like 錦の御旗に掲げる.
He used 'reform' as his noble banner to suppress the opposition.
More and more companies are using environmental protection as their worthy cause.