Signal is TWICE's 4th Mini Album, released May 15, 2017 through JYP Entertainment, featuring the lead single "Signal." It comes in three versions — A, B, and C — with version C sharing a photobook design with either A or B, making it a notable quirk for completionists. Each copy includes an 88-page photobook, CD (1 random of 9), photocard (1 random of 27), special photocard (1 random of 9), and a photo print (1 random of 3). The large photocard pool of 27 across all versions gives this one a lot of pull variety. A monograph was released November 7, 2017, featuring a 150-page photobook, ~40-minute behind-the-scenes DVD, and notably, 9 signed member photocards — making it one of the more desirable monographs in the discography