Mike - I don't know anything about this, but I did find a newspaper article from this time period referring to letters marked "Revisada por el censor." The newspaper was from Veracruz, about as far from Sonora as you can get in Mexico, but perhaps this helps. As I read it, the article supports the Revolution and complains that the people do not appreciate it. Here is the relevant paragraph and my preliminary and rough translation:
El Pueblo (Veracruz Mar. 15, 1915)
On page 3 an article appears, the first paragraph of which refers to the censorship of letters at this time. Unfortunately the title of this article is cut off, but it is signed by Jorge Useta.
Uno de los enemigos más poderosos que tiene una Revolución tan transcendental como ésta, es el egoism ambiente. (Con permiso de la Física, le tomamos el adjetivo.) Uno de los enemigos más poderosos que estorban incesantemente la acción revoluncionaria, es la exigencia perentoria que la Revolución se le hace por el vulgo, de los frutos de bienstar que la Revolución tiene prometidos. El vulgo razona así con mucha frequencia: “Tú, Revolución, me ofreces libertad, y me abres las cartas poniéndoles con toda frescura un ‘Revisada por el censor.’ Luego no me das libertad.” …
One of the most powerful enemies a Revolution as momentous as this one has is ambient egoism. (With permission of physics, we take the adjective). One of the most powerful enemies that incessantly hinders Revolutionary action is the peremptory demand made by the people for the fruits of well-being that the Revolution has promised. The people thus reason with much frequency: “You, Revolution, offer me freedom, and [yet] you open the letters to me, putting [on] them with much cheek ‘Examined by the censor.’ Then you do not give me freedom.” …