This marking was used to cancel stamps in the Empire Non Dentele issue (it had been in use since 1852). There are a little over 4,500 different petits chiffres, which makes collecting them very interesting, and also daunting.
This is what Google AI says about this marking (first in French, then translated to English):
Les "Petits Chiffres" sont un type d'oblitération postale utilisé en France à partir de janvier 1852 pour annuler les timbres-poste. Il s'agit d'un losange composé de petits points numérotés qui a remplacé les oblitérations précédentes.
Voici des points clés concernant les oblitérations "Petits Chiffres" :
Période d'utilisation : Ils ont été introduits en 1852 et ont été progressivement remplacés par les "Gros Chiffres" à partir de 1862-1863, bien que certains aient pu être utilisés plus tard.
Structure : Le cachet est en forme de losange formé de points, avec un numéro à l'intérieur identifiant le bureau de poste d'origine.
Identification : La liste des bureaux de poste français est classée par ces numéros, indiquant le nom du bureau (souvent l'actuel avec l'ancien entre parenthèses) et le département.
From Google Translate:
"Petits Chiffres" (Small Numerals) are a type of postal cancellation used in France starting in January 1852 to cancel postage stamps. It consists of a diamond-shaped pattern composed of small numbered dots, which replaced previous cancellation types.
Here are some key points regarding "Petits Chiffres" cancellations:
Period of Use: They were introduced in 1852 and were gradually replaced by the "Gros Chiffres" (Large Numerals) starting in 1862–1863, although some may have remained in use for a time thereafter.
Structure: The postmark is diamond-shaped and formed by dots, with a number inside identifying the originating post office.
Identification: The list of French post offices is organized according to these numbers, indicating the name of the office (often the current name, with the former name in parentheses) and the department.
Here is an example from 1857:
Here is a detail of the postmark:
Here is the stamp, postmarked with a Petits Chiffres.
2082 corresponds to Montereau in the Seine-et-Marne department. This stamp has some plate flaws. The right edge shows some wear. This sometimes happens to stamps on the right edge of the plate.
The top left and bottom right cartouches have minor plate wear.
Here is the back of this cover and the commercial letter it carried.
Here is the commercial bill:
