\version "2.6.0"

#(ly:set-option 'point-and-click #f)

\paper {
  indent = 0
}

{
  \override Score.RehearsalMark #'break-visibility = #begin-of-line-invisible
  \time 3/4
  a b c
  \override Score.RehearsalMark #'self-alignment-X = #LEFT
  \mark \markup { \large {"BLAH" } }
  a b c
  \override Score.RehearsalMark #'self-alignment-X = #RIGHT
  \mark \markup { \large { "BLAH" } }
  a b c
  \override Score.RehearsalMark #'self-alignment-X = #2
  \mark \markup { \large { "BLAH" } }
}