I bought this t-shirt in the Chapultapec Castle gift shop.
It shows the Mexican flag known as ‘el Doliente Hidalgo’ (the Suffering of Hidalgo).
Father Hidalgo was a priest who spoke out against the French treatment of Mexican peons.
He was arrested by the French and tortured for several weeks and finally executed by strangulation.
This flag, carried into battle on 5 Mayo 1862, carried the message that the French would suffer as they made Father Hidalgo suffer.
That is: no mercy and no prisoners.
I bought it and then looked up its history when I got back to my hotel and like it even more now that I know the history.