The script's signs include bones, dynamites, skulls, dinosaurs, fish, eyes, and a UFO. Most of them are things that have to do with Gokudera's experiences and interests. Each symbol represents a hiragana character. When Tsunayoshi Sawada first saw it, he said that it looked like drawings to him.
The first time G-Letters were seen was during the Future Arc, when Gokudera found a message written in G-Letters among his future self's belongings. It was a message to gather all of the tenth generation Vongola Guardians.
Gokudera also wrote something on his notes in G-Letters when Shitt P! first introduced herself to the class.