Do the marks signify the second house within schedule number 158 ?
That's indicated by a single slash (/) between households, and a double slash (//) between dwellings.
I can't see any separation between the two houses on that schedule number. In most (maybe all) of the 1881 census pages I have, anywhere there is a single slash to denote a new household there is a new schedule number.
Got my slashes the wrong way around!
There is a double slash (\\) before Joseph B Finch and another after Maria Moore.
Looks to me like a Lodging House?