Time signature in parentheses

Enclose the time signature in parentheses.

\version "2.24"

\relative c'' {
  \override Staff.TimeSignature.stencil = #(lambda (grob)
    (parenthesize-stencil (ly:time-signature::print grob) 0.1 0.4 0.4 0.1))
  \time 2/4
  a4 b8 c
}