The bit was called Actual Items. On Conan, they did it by taking real ads and adding obviously fake, funny text to them that the camera would zoom in on to reveal (like an otherwise normal ad for Mayonnaise with a caption it would zoom on that goes 'Remember, a man who can't get mayonnaise at home will go looking for it outside the marriage').

What always made me love the bit and it's ripping-on-Leno-ness is how Leno always repeatedly points out that his are real headlines, and Conan would do the exact same thing, pointing out that if these were made up, they would just be wasting everyone's time.

Interesting fact: the bit was created by Louis CK while he was writing for the show, and it was even a segment on the very first Late Night.

"And again, these are totally real, you can't make these up"
ad infinitum