  We use the factorization constraints of open-closed string field theory to
determine the signs and normalizations of general string amplitudes with both
open and closed string external states. The normalization of all amplitudes is
controlled by the genus, the number of boundaries, the number of open and
closed string insertions, the string coupling and the D-brane tension. The
challenge with signs arises because the relevant moduli spaces are not complex
manifolds and have no obvious orientation. We deal with this by fixing a
specific convention for the sign of the integration measure over the moduli
space and adopting a consistent prescription for the ordering of operators and
ghost insertions inside correlators.
