Steve knew the feeling of being watched. You walked around with Captain America's shield and people stared. But he also knew the feeling of being watched without seeing anyone there. The kind of prickle on your neck, like a damn deer waiting for an arrow or a bullet. So Steve was aware and Bucky wasn't exactly invisible, he wasn't The Winter Soldier anymore, but he was apparently lurking in the shadows outside his house.
It wasn't hard to climb out the back window and circle around, he was light on his feet and Steve approached from the left, watching Bucky watch the door. "You gonna knock or-?" He asked with his eyebrows raised.
He looked like Bucky, his Bucky, the one that had gone and left him again. But he was solid, like Peter was again. Maybe that's why he let himself think this was him, not another version or someone from somewhere else the same but different. "You out here working on that pout?" He added after a pause. Obviously Bucky was watching him and maybe that meant they had the same questions.