"And yet I find you back here. Guess I must miss you on your days out."

To provide the opposite, Sirius isn't one to really keep tabs on people. Save those he feels he needs to keep an eye on and a old ghost isn't one of them. He figures that Rorschach can take care of himself, and outside of passing on, there wasn't much that a ghost could do. At least, not that he'd seen.