The real stuff
Bosco is a brand of chocolate syrup that was introduced in 1928. It is also the ATM code of George Costanza, as seen in “The Secret Code”.
Story[]
George is unwilling to tell anyone his ATM code, even his fiancée Susan, who tells him it is a sign of trust for him to tell her his code. George told Jerry that he would give him his code should Jerry find himself in a situation where some fast cash will save his life.
While looking after Mr. Peterman's mother, he falsely thinks she is unresponsive, and takes her to the hospital. George decides to tell someone his code; he tells her. She wakes up saying “Bosco” louder and louder and shortly after she does this, she dies. Peterman tries to find out what this means, but cannot figure it out. When George is with Peterman, they find a man trapped in the bank, which is almost on fire, and his sleeve is stuck in the ATM. In order to be set free, the man begs George for his code, which he reveals, and the episode ends. Albeit speculation, it is likely that Peterman yelled at George for not saying that he told his mother that his secret code was “Bosco”.
Bosco also appears in “The Baby Shower”; it is all over a shirt that George's past girlfriend stained. He confronts her about this at the baby shower.