"Warning" is a song by the American rock band Green Day. It is the second single and title track from their sixth album of the same name. Billie Joe Armstrong has said that the original concept was to create a song whose lyrics were made up of all signs and labels, and the idea grew from there. The song was played for the first time during Bridge School Benefit played acoustic in 1999. This is the first Green Day song to feature a tremolo effect on the guitar; an effect used prominently in the 2004 single "Boulevard of Broken Dreams".