What is the correct punctuation for Mlle?

"Mlle" is an abbreviation for "Mademoiselle," a French title of respect used for an unmarried woman. As an abbreviation, it doesn't require any punctuation.

However, it's important to note that using "Mlle" is considered outdated and potentially disrespectful in modern French society. It's generally preferred to use "Madame" or "Mademoiselle" in full, or simply address the woman by her name.