Signal (Korean: 시그널) is a South Korean television series written by Kim Eun-hee, directed by Kim Won-seok, and starring Lee Je-hoon, Kim Hye-soo, and Cho Jin-woong. It was inspired by real-life criminal incidents in Korea, including the Hwaseong serial murders. The first season aired on tvN from January 22 to March 12, 2016, every Friday and Saturday at 20:30 (KST). In March 2024, a second season was confirmed to be in production.

The series received widespread acclaim from audiences and critics alike for its story and performances. It is also one of the highest-rated Korean dramas in cable television history with a peak audience viewership of 12.544% - only next to Reply 1988 (18.803%) at the time of its release in 2016.