\version "2.11.38"

\relative c'' {
  \once \override TrillSpanner #'bound-details #'left #'text = 
      #(markup #:line (#:halign -0.5 #:musicglyph "scripts.trill" #:teeny #:raise 0.65 #:sharp ))
  b1\startTrillSpan b\stopTrillSpan
  
  \once \override TrillSpanner #'bound-details #'left #'text = 
      #(markup #:line (#:halign -0.5 #:musicglyph "scripts.trill" #:teeny #:raise 0.5 #:flat ))
  c\startTrillSpan c\stopTrillSpan
}