When my wedding invitation arrived, I thought I understood everything on the response card. The date was clear, the venue was familiar, and the meal choices were printed neatly below. But one tiny detail stopped me: a single capital “M” followed by a blank line.

I stared at it longer than I should have. Was I supposed to write my first name? My full name? Was the “M” connected to the meal choices somehow?

I eventually asked a friend, and the answer was surprisingly simple. On traditional RSVP cards, the “M” is generally the beginning of a courtesy title—such as Mr., Mrs., Ms., or Miss. The blank line that follows is where the guest writes their name, completing the appropriate title and name.

So, for example, someone might write “Mr. John Smith” or “Ms. Jane Smith,” depending on the format of the card and their preferred title.

The tradition comes from older formal invitation etiquette, when titles were commonly used when addressing guests. Today, many invitations have modern wording and may skip the “M” entirely, but you can still find it on formal wedding stationery.

The first time I learned this, I couldn’t help but laugh at how such a tiny letter had caused so much confusion.

Sometimes wedding etiquette hides its biggest mysteries in the smallest details—and that little “M” is a perfect example.