Zombie Elvis Found!
Basically, "Zombie Elvis Found!" is a headline on newspapers that are found on the streets throughout Liberty City and Vice City. The newspaper depicts the headline, along with a black and white photograph of Elvis' face.
This is an in-game joke towards the hysteria that revolved around the alleged "sightings" of Elvis during the 70's and 80's after his death. He is never seen walking around the streets of Liberty City and/or Vice City.
Elvis was also mentioned several times in Grand Theft Auto 2, for example, player can find a group of Elvis impersonators walking in the street. Running them down without braking grants a large money reward along with the words "ELVIS HAS LEFT THE BUILDING" being spoken and displayed in the middle of screen. Elvis itself is also featured in GTA 2 opening movie, singing in the bar. However, Zombie Elvis didn't make any appearance in the previous GTA games.