But why would the Mafia care if you took photos? Money laundering would happen behind the scenes, in the accountants office.

Definitely agree that something is shady though. Not sure what, but this reminds me of a recent article on 'The Big Mac' index, which is used as an alternative measure of inflation. Perhaps McDonald's is under orders by the French government to prevent people from taking photos of their menus (and consequently their burger prices) to hide serious inflation problems. ;)

On a side note, if you are going to be in Paris on vacation, the food capital of the world, why the hell are you eating at McD's?