Spanish to English Social Sciences Cinema, Film, TV, Drama Film review

It seems to me that "un cartel" here means nothing more than "a text" and that the posted term could therefore me translated as "text appears on the screen informing viewers that what follows is..." or "a title appears informing viewers that what follows is..."

I am interested in two things here:
1.
Confirmation of one of my alternatives, or the suggestion of a better translation.

2.
The English translation of "cartel" in a cinematic context.

Thank you.

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Al comienzo de la película, ***un cartel avisa que está*** “basada en presuntos hechos reales”, y que los escenarios e incluso los personajes lo son, con la excepción del sótano donde se preparó el atentado, que quedó destruido por la explosión y que por tanto no ha podido ser utilizado como set de rodaje.