Kilroy was here

Well, not Kilroy, but Caspar.
We have a half door on the top of our stairs, between the floor where we mainly are and the ground floor (with other rooms).
Often when we go down leaving Caspar alone and then return he has his muzzle on top of the door.
And often that makes me think "Kilroy was here".
It looks so cute and it is so nice to be welcomed by that little chap.