Make your moment easy to recognize.
Name the set, then the moment
The artist and event date are more useful than “the person in black.” Add the stage and a rough time, without naming someone else.
Make room for the details that matter
Was it before the opener, during a particular song, or on the walk out? Explain your conversation rather than describing a stranger’s body.
Leave one detail off the poster
Ask about an unexpected song choice or a joke from the conversation. A convincing answer is a clue, not identity verification.