  Values of quaternionic modular forms are related to twisted central
$L$-values via periods and a theorem of Waldspurger. In particular, certain
twisted $L$-values must be non-vanishing for forms with no zeroes. Here we
study, theoretically and computationally, zeroes of definite quaternionic
modular forms of trivial weight. Local sign conditions force certain forms to
have trivial zeroes, but we conjecture that almost all forms have no nontrivial
zeroes. In particular, almost all forms with appropriate local signs should
have no zeroes. We show these conjectures follow from a conjecture on the
average number of Galois orbits, and give applications to (non)vanishing of
$L$-values.
