In the Reborn! Fandom, several characters' names have either a number (i.e. Tsuna is 27), a letter (i.e. Lambo is L), or an abbreviation (i.e. Genkishi is Gen). Not all characters as of yet have an assigned shorthand, and several may overlap, which usually results in finding new ways to manipulate pronunciations, sometimes even using other languages numbers (i.e. Uni is Latin for 1, so her number is 01).
Numbers
Tsunayoshi Sawada: 27
Hayato Gokudera: 59
Takeshi Yamamoto: 80
Ryohei Sasagawa: 33
Kyoya Hibari: 18
Mukuro Rokudo: 69
Chrome Dokuro: 96
Basil: 84
Lal Mirch: 66
Superbia Squalo: 29
Fran: 26
Lussuria: 64
Tetsuya Kusakabe: 93
Haru Miura: 86
Fuuta: 2
Hana Kurokawa: 87
Nana Sawada: 77
Shoichi Irie: 51
Spanner: 48
Doctor Shamal: 50
Bianchi: 88
Ken Joshima: 14
Chikusa Kakimoto: 49
Uni: 01
Byakuran: 100
Ghost: 52
Kikyo: 99
Bluebell: 06
Zakuro: 39
Torikabuto: 16
Daisy: 04
Glo Xinia: 56
Gamma: 57
Enma Kozato: 00
Suzuki Adelheid: 20
Shitt P.: 40
Kaoru Mizuno: 31
Koyo Aoba: 54
Rauji Ooyama: 62
Julie Katou: 11
G.: 02
Letters:
Lambo: L
I-Pin: I
Giotto: G
Xanxus: X
Viper: V
Belphegor: B
Kyoko Sasagawa: K
Reborn: R
Dino: D
M.M.: M
Skull: S
Fon: F
Aria: A
Abbreviation:
Lambo: Lam
I-Pin: Pin
Genkishi: Gen
Levi A. Than: Lev
Lanchia: Lan
Colonello: Col
Verde: Ver
Luce: Luc