Meredith Grey and Derek Shepherd's wedding Post-it note continued to play an important part in Meredith's story as it made a surprising return in season 19 of Grey's Anatomy. First appearing in the season 5, episode 24, "Now or Never", the wedding Post-it note was an idea concocted by Derek after he and Meredith decided to get married but struggled to attend their appointment at City Hall. With so much drama and chaos unfolding at the hospital, Derek told Meredith that they should write their marriage vows down on the Post-it note and then sign it to seal their commitment to one another.
Although Meredith and Derek officially got married in season 7's "White Wedding", the blue Post-it continued to play an important part in their relationship as the couple occasionally referred back to their it whenever they got into fights and were on the verge of breaking up. It was the perfect symbol of their love and showed everyone why they were each other's perfect match. Sadly, after Derek's death, the Post-it was retired in season 13 as Meredith took it off the wall and put in a safe space.
However, this wasn't last time fans saw it as the writers brought it back in season 19 for one more pivotal scene.
Meredith and Derek's Post-it note made a return in season 19, episode 6, "Thunderstruck", after it was rescued from a housefire by her sister, Maggie.
Although Meredith was about to move to Boston with her three children, Zola, Bailey, and Ellis, the writers couldn't resist tormenting their protagonist further as her house was almost burned to the ground in a lightning storm. While all her relatives and loved ones managed to escape the blaze unscathed, Meredith sadly lost several important mementos, including Derek's ferry boat cap and his tumor on the wall drawing. The only thing that could be salvaged was their framed blue Post-it wedding vows.
Out of all the mementos to be saved from the fire, it is rather significant that the writers chose Meredith and Derek's Post-it as it seemed to suggest that the love Meredith had for Derek could never be destroyed (which isn't surprising since the limbo-like dreams Meredith had in season 17 of Grey's Anatomy emphasized that her love was transcendental). Saving the Post-it also seemed to emphasize the fact she will always carry this love with her wherever she goes (whether that is to Boston, Washington, Seattle).
The Post-it note making an appearance in season 19's "Thunderstruck" also seemed to hint that there was trouble ahead for Meredith and Nick's relationship as new secrets were revealed. Not only did Nick discover that Meredith was about to move to Boston without discussing it with him, but he was also hurt that she didn't tell him that Derek's nephew, Lucas, was also at the hospital.
Tensions between the two increased even further when the next episode, "I'll Follow the Sun", saw Meredith pretend that she didn't hear him confess his love for her just as she was flying to Boston.
Between the two episodes of Grey's Anatomy, it seemed like Meredith had a change of heart about their relationship as the blue Post-it note caused her to re-evaluate her life and the choices she was making. Although Meredith did love Nick, the Post-it note reminded her of all the promises she and Derek made about what kind of life they wanted for themselves and their children.
No matter how much she wanted to fight be with Nick, Meredith was happy that she was making the right choice as it was going to Boston benefited Zola, Bailey, and Ellis' futures in the long run.