It must be preceded by the expression : "Best before…", but also sometimes follows the letters "Exp" (for Expire), or simply written as it is without warning expression.
According tothe new European Regulation governing cosmetics (which replace the former Directive), it may be introduced by a symbol with the form of an hourglass.

Legally it is composed of, in order, either the month and the year, or the day, the month and the year.
Attention! This is not a deadline for selling, thus it is important to check the date prior to buying the product: generally the date appears next to the batch number.

This is compulsory for cosmetic products only if minimum durability is inferior to 30 months. For the products that have alonger ‘lifespan’, only the indication of the period-after-opening is necessary.

It may be noted that this principle may lead to some questions.
Who can say that a product  with a durability inferior to 30 months can remain open and be used for example 24 months later without damage ?
Another example: imagine a cosmetic product with a durability superior to 30 months. Legally it shows it can be used until 6 months after the first opening (  6 M as an open jar ). Imagine that same product, sitting on the shelf of a small beauty salon in which the stock "runs" slowly, or which has been forgotten and found in the back of the bathroom cabinet. Do you think you can calmly use a cream of 3, 4, 5… 10 years of age? What can happen to it after so much time ?
If we pay attention, we might think that lawmakers haven't considered that a cosmetic product doesn't keep in the same way before and after its opening. In the end these two indications are very different, they are both indispensable for the safety of comsumer and they both should be compulsory on all products. Some manufacturers go beyond the law and write the two dates: this is a good initiative.