As guidot says, it's odd this isn't already included (at least, not that any of us three can apparently find). It should be an easy fix, so you might want to mention it to them! Here's one possible workaround:
\version "2.19.48"
global = {
\key c \major
\time 4/4
}
upper = \relative c'' {
\global
R1 |
}
lower = \relative c {
\global
<g g'>4_\markup + r_\markup { \char ##x2A01 } r2 |
}
\score {
\new PianoStaff <<
\new Staff = "upper" \upper
\new Staff = "lower" { \clef bass \lower }
>>
\layout { }
}
I just used a _\markup +
for the first symbol. For the second symbol, I tried to find a Unicode equivalent with _\markup { \char ##x2A01 }
, but this was the best I could find. (If anyone finds a better one, please let me know!)