Spenceley, who can also operate in defence when called upon, has agreed terms with the club after impressing during recent pre-season friendlies.
His latest outing came as a substitute against Blyth Spartans, where he put on a composed display against National League North opposition.
"Sam's a local boy who has come in over pre-season. He's done really well when we've watched him, both in matches and in training," Blues manager Nathan Haslam said.
"We can see potential in Sam and we've signed him on with the hope of developing him while he's with us, as well as giving him the chance to play for his hometown club."
Photo credit: Whitby Town