Here again with a better 'minus' look:
\version "2.18.2"
#(set-global-staff-size 50)
plus =
#(define-music-function (parser location fingering) (ly:music?)
(let ((music (make-music 'FingeringEvent))
(finger (ly:music-property fingering 'digit)))
(set! (ly:music-property music 'tweaks)
(acons 'stencil
(lambda (grob)
(grob-interpret-markup grob
(make-concat-markup
(list
(markup #:lower 0.3 (#:tiny "+"))
(number->string finger)))))
(ly:music-property music 'tweaks)))
music))
minus =
#(define-music-function (parser location fingering) (ly:music?)
(let ((music (make-music 'FingeringEvent))
(finger (ly:music-property fingering 'digit)))
(set! (ly:music-property music 'tweaks)
(acons 'stencil
(lambda (grob)
(grob-interpret-markup grob
(make-concat-markup
(list
(markup #:line
(#:translate
(cons 0.1 0.5)
(#:override
(cons (quote thickness) 2.2)
(#:draw-line (cons 0.6 0)))))
(number->string finger)))))
(ly:music-property music 'tweaks)))
music))
{
gis'-\tweak ParenthesesItem.font-size #-4 -\parenthesize-\plus-2
g'-\minus-2
}
Cheers,