"Signal" is a song written by Ma-saya, Joker, Joey Carbone, Lisa Huang and Akira for the second single and second studio album of the Japanese boy band, KAT-TUN.

The single was released in two pressings - a regular version with instrumental versions of all the songs and a limited edition containing the songs, the music video of the title track and a short film of the making of the music video.

[1] The single was used in a commercial for NTT DoCoMo's FOMA "9 Series" cell phone which all KAT-TUN members starred in.

KAT-TUN performed the song on television for the first time on Utawara, a variety talk show where they were already regulars alongside senpai Jun Matsumoto of Arashi, on July 16, 2006.

Music Champ the day after and made their second appearance on Masahiro Nakai's Utaban on July 20.