Both a extremely well written and directed tvN shows that both aired in 2016. Both focus on cases that seem irrelevant at first but tie up really well by the end. Though I would personally favor Signal for its unique time travel aspect and how it moves on from case to case almost effortlessly, Pied Piper does not disappoint in the least. The thrill both shows give, specially in the latter half is wonderful. If you liked one, you'll love the other.