  We compute a class of gauge invariant observables for marginal solutions and
the tachyon vacuum. In each case we find that the observables are related in a
simple way to the closed-string tadpole on a disk with appropriate boundary
conditions. We give a sketch of an argument that this result should hold in
general using the BRST invariance of the closed string two-point function.
Finally, we discuss the analogous set of invariants in the Berkovits
superstring field theory.
