"Level Two, Department of Magical Law Enforcement, including the Improper Use of Magic Office, Auror Headquarters and Wizengamot Administration Services."
"This is us, Harry," said Mr Weasley, and they followed the witch out of the lift into a corridor lined with doors. "My office is on the other side of the floor."
Harry Potter and the Order of the Phenix
According to the context, "this is us" seems to mean that they had arrived at their floor. But I feel "this is ours" should be used for this. What does "this is us" truly mean here?