Vault 106. It seems to have been written by one of the insane people inhabiting the vault. This note can be found on a table in the living quarters near the overseer's office.
Scribbledy bibbledy hoodelly hoo.
Wing wang bricka bang choo choo choo.
Upsideup popsicle tastes like blue
Ghosts in the hall go boo boo boo!