Bookmarks upside down in Vile Bodies (5)
I believe the answer is:
Here is my best explanation:
'bookmarks' is the definition.
I know nothing about this answer so I cannot tell whether it can be defined by this definition.
'upside down in vile bodies' is the wordplay.
'upside down' says the letters should be written backwards.
'in' indicates a hidden word.
'ilebo' can be found hidden inside 'vile bodies'.
'ilebo' reversed gives 'OBELI'.
(Other definitions for obeli that I've seen before include "Textual indicators", "Signs of death", "Marks on script", "Dagger signs in printing", "Dagger-shaped signs", "signs of publishing", "Dagger signs for footnotes", "They refer to bottom", "signs of doubt" and "daggers drawn".)