Prism-gram

The Prisogram is a prism-like object that sends mail in the Land of Ooo, or possibly only from the Crystal Dimension. Once someone has written a letter, they swipe the Prisogram on the paper and it absorbs the writing. Then it converts the letters into brain waves and shoots them onto one's forehead, just like a laser. So far, it has only appeared in the Season 2 episode "Her Parents," where Jake uses it to send a message to Lady Rainicorn's parents, Bob Rainicorn and Ethel Rainicorn.

Trivia
It seems that it can really hurt once the letter (in the form of a laser) is shot at the forehead (Jake seemed to flinch and became weak for a second in the process.)

the letter jake wrote means "To Mr.Rainicorn and Mrs.Rainicorn, Rainroad 47. Please come here early one hour at lunch. I haven't a pet turtle. from Jake." and in korean "무지개콘 선생님과 사모님께, 47 무지개 길. 점심에 한시간 일찍 와주세요. 나는 애완 거북이가 없어요. 제이크 드림"