"Douane" means customs - coupled with the holes that must have had string or ribbon - it must have been a customs seal.
Its a lead seal. a piece of wire would go through the two holes before it was pressed with the seal pattern. the wire has rotted away. It is a tamper resistant device. This type device is still used today, in fact I use them on a daily basis as a Sealer of Weights and Measures
Yes, that is a customs seal, apparently for agricultural products - I seems to read 'Douane des fermes' which means 'agriculture customs office'. Leads seals like this were used to officially seal bags of products. Yours seems to be quite old and dates, as it seems, before the french revolution. First I have seen.
The side with the ship says "Doua(n)ne de Paris", I think. The city's CoA has a ship and the fleurs-de-lis, and that is apparently depicted on that side ... Christian
