  A color-flavor-spin singlet state of six quarks $uuddss$ ($S$, or sexaquark)
has been argued to be a potentially undiscovered deeply bound, long-lived
hadron. Theoretical calculations of the $S$ mass have been made in the
literature, widely varying from deeply-bound $\sim 1.2$ GeV to weakly-bound
$\sim2.2$ GeV. Given the spread of the mass predictions, it is vital to derive
observational constraints on the state as a function of the mass. The
transition rates between $S$ and two baryons are governed by $\tilde{g}$, the
effective Yukawa coupling between $S$ and two baryons with the same quantum
numbers as $S$. In this paper, we place strong observational constraints on
$\tilde{g}$, improving on various previous limits; additional limits assuming
$S$ is dark matter are also presented.
