If I am downstairs they will simply leave the room and head to the back door and come back and then leave the room and head to the back door. Eventually I, the human, will catch on.

If I am upstairs Ripley will start walking in little circles and looking at me. Bella rarely asks when we are upstairs but, for the few times that she has, she just walks over to me and does a little muffled growl, sort of sounds like ERRR.