Rabbit in a Snow Storm - S1-E3
Continuity mistake: Turk is showing off a pistol at the start of the episode to John before buying it. Before he says the gun will not jam, he is pointing it to his left, but when he says his name in the angle change, it's pointed to the right. (00:02:00)
Chosen answer: After some research, I can say that no, Cass is not a character of Marvel, nor is he present in the Netflix show. As far as I can tell, it's either a real person, or a random name chosen for the coffin, most likely the former. In another season of Daredevil, the show utilized a real cemetery displaying real names in the tombstones.