The most famous audio "piece" associated with these countdowns is the "2-pop" —a single 1 kHz tone that occurs exactly 2 seconds before the first frame of the movie to ensure sound synchronization. Where to find these pieces
In the context of "Cuenta atras cine" (Cinema Countdown), you are likely looking for the or the SMPTE Universal Leader . These are the numbered countdowns (starting from 10 or 8) used by projectionists to focus the projector and frame the film before the movie begins.
Early films were silent, but screenings were often accompanied by live piano or organ music. There was no single "theme song" for cinema in 1895, though popular operettas and marches of the time were common accompaniments. "Cuenta Atrás" (Film Countdown)