Official BBC spoiler alert
This is literally the Klaxon indicating that a portion of the podcast is going to be dedicated to a spoiler-tastic review of a film. This started with Star Wars: The Force Awakens on 8th January 2016.
Said with feeling and passion, but without taking the mickey: "<KLAXON> Warning, official BBC spoiler alert. This section of the Kermode and Mayo Film Review Podcast contains <insert film name here> spoilers. <KLAXON> If you don't want to hear them please stop listening now. Thank you...... Were you not listening? Turn it off! <KLAXON>"
This will be followed up by "<KLAXON> Spoilers imminent! <KLAXON> Spoilers imminent! <KLAXON> Spoilers imminent! <KLAXON>" just before the actual film spoiling begins.