If you are asking about a specific piece of related to the character Lisbon (Raquel Murillo), it might be the mystery note from the series finale.

Are you interested in a on how to fold the Professor's specific origami bird?

While Season 2, Episode 3 focuses on the police trying to identify the Professor's fingerprints at the pharmacy and his attempt to escape a police station, the is a recurring symbol throughout the show. 🎭 The Significance of the Paper

You're likely thinking of the that is a signature of The Professor in the series Money Heist ( La Casa de Papel ).