Therefore he couldn’t deliver his message verbally and he knew he was going to die so his only option was to send Pa as a messenger and the quickest, most safe way for the message to be delivered was if it was literally etched in his person so that he wouldn’t lose the message. He also wrote it in code.
It’s a letter from the Japanese language ‘Katakana’ that reads as “ta”. By which he meant his book’s name ‘make out tactics ‘. By 31,8 , Jiraya meant 8th word of 31 page no. By 106,7 , he meant 7th word of 107 page no.