Many guests have probably noticed a mysterious standalone letter printed on formal RSVP cards and wondered what it means. At first glance, it can look like some kind of code related to meal choices, the number of guests attending, or even a way for the host to track attendance.

In reality, the letter is usually much simpler than people expect. On traditional RSVP cards, a single printed letter—often the beginning of a title—is meant to serve as a prompt for the guest. It reminds you to fill in the appropriate form of address before writing your name.

For example, the printed “M” can be followed by “Mr.,” “Mrs.,” or “Ms.,” depending on the guest’s preferred title. After completing the title, the guest can write their name on the line, allowing the host to clearly identify who is responding to the invitation.

This small detail is a leftover from more traditional formal stationery and invitation etiquette. What may initially look like a strange symbol or hidden code is actually just a simple writing prompt. Sometimes, the little details on formal invitations have a much more ordinary explanation than we imagine.