Positioning a segno relative to an alternative line

[Jacques Menu]

Hello folks,

In the attached, I’d like the segno to be below the second alternative line in 
the third system.

I tried:

      \once \override TextScript.extra-offset = #'( 0 . -5.0 )
      \mark \markup { \musicglyph #"scripts.segno" }

but to no avail.

Thanks for your help!

JM

LaPiemontaise.pdf
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