Unicode character for marking
===

We are going to digitize a lot of books. We want indicate place of line break in original book. Which invisible Unicode charter can be used to mark some special places in a raw file?

    This  is  a  sentence 
    in original book that
    I want mark      line
    break places.

what is proper character to replaced with *:

    This  is  a sentence * in original book that * I want mark line *break places.