1. The semicolon tattoo Clay gets in Season 2 represents suicide prevention as part of Project Semicolon's mission.
2. Alex has a poster of Joy Division's "Love Will Tear Us Apart" on his bedroom wall. The song was featured on the Season 1 soundtrack and played when Tony gave Clay a ride home.
3. Speaking of Joy Division, "Love Will Tear Us Apart" starts off Season 1, while Season 2 begins with "Love Vigilantes" by New Order. New Order was formed by members of Joy Division after their lead singer, Ian Curtis, killed himself.
4. Justin's postcard to Jessica that references Nancy and Sid is a callback to their costumes in Season 1 when they dressed up as Sid Vicious and Nancy Spungen.
5. The day of the spring fling dance is April 20, which is the anniversary of the Columbine High School shooting and the day thousands of high school students protested gun violence by walking out of class this year.
6. The writing on the back of the Polaroids that Clay receives is written in the same shade of blue as the nail polish Hannah used on the tapes.
7. Both Zach and Clay, two of the most important people to Hannah, absolutely love Mike and Ike's. Clay wishes they could hang out and eat them again, while Zach always ordered them when visiting Hannah.
8. When Cyrus meets Tyler, he mentions that he saw a photo of a dog peeing that Tyler had taken. The comment is a direct nod to a moment in Jay Asher's novel.
9. Someone wrote that they wished they could still get hot chocolate with Hannah, a callback to Alex, Jessica, and Hannah's dates to Monet's in Season 1.
10. The photo of Hannah on her locker from Season 1 appears to be part of the photoshoot Tyler does with her in Season 2.
11. The book Zach reads while dating Hannah, The Art of Fielding by Chad Harbach, is about a group of baseball players and the relationships they form. Season 2 of 13RW deals with the actions of Liberty High's baseball team.
12. The baseball team wears number 16 on their jerseys in honor of Jeff Atkins.
13. When Mrs. Baker gives Clay the list of "13 Reasons Why Not" she found, you can read that Hannah thought she and Clay might've been meant for each other.
14. Hannah has The Hunger Games trilogy on her bookshelf in her room.
16. In Hannah's notebook, you can see parts of a poem about Clay that she wrote. The poem was also visible in Season 1.
17. Finally, if you look closely, it appears that cassette tapes are no longer part of Baker's Pharmacy's inventory.
