Fans were left less-than-impressed when Detective Sergeant Steve Arnott revealed he had noticed Dot Cottan tap out 'H' in Morse code during his dying declaration on Sunday's Line of Duty.

While the colored lines found on new tires are optional, follow along to see what they mean, and why they are there.

Line of Duty: All the unanswered questions after Season 5's epic finale Arnott continued: "The letter h in morse code is four dots. H is not an initial, it’s a clue. Four dots, four caddies ...

Looking at Dot's tapping fingers, DI Kate Fleming (Vicky McClure) explains: "It’s Morse code. Dot dot dot dot.” Steve adds: “The letter H in Morse code is four dots.