Wedding registries - the Why
When I photographed my mate's wedding in the local registrar's office they said take whatever photos you want (including using flash - try that in a church !!). Only rule was no photographing allowed when they signed the register. Why - because the flashgun distracts the people signing and since it is a legal document they need to sign it without distractions. Afterwards it was OK to photograph them (same register, just play acting with a fancy quill instead of the Bic they used to actually sign with).