Vim has a number of invisible characters that you can set.
One of those characters is the end of line (eol) character.
Whatever character you
set this to will appear at the end of each line in your file. This is great
for highlighting extra whitespace at the end of a line that would otherwise
appear invisible.
Set the eol invisible character like so
:set listchars=eol:¬
or append it to the existing list of invisible characters like so
:set listchars+=eol:¬
See :h listchars to see what other invisible characters you can set.