it took my a while before I could remember but here is the appropriate law for such case:
Article 719 (Civil Code). Whoever finds a movable, which is not treasure, must return it to its previous possessor. If the latter is unknown, the finder shall immediately deposit it with the mayor of the city or municipality where the finding has taken place. The finding shall publicly be announced by the mayor for two consecutive weeks in the way he deems best.
If the movable cannot be kept without deterioration, or without expenses which considerably diminishes its value, it shall be sold at public auction eight days after the publication. Six months from the publication having elapsed without the owner having appeared, the thing found, or its value, shall be awarded to the finder. The finder and the owner shall be obliged, as the case may be, to reimburse the expenses.