–30– has been traditionally used by journalists in North America to indicate the end of a story. It is commonly found at the end of a press release. There are many theories about how the usage came into being, e.g. from that number's use in the 92 Code of telegraphic shorthand to signify the end of a transmission in the American Civil War era.
In Quebec, a journalism magazine is called -trente-, the French word for thirty.
In popular culture
For consideration: John 19:30 New International Version (NIV) 30 When he had received the drink, Jesus said, “It is finished.” With that, he bowed his head and gave up his spirit.
References
–30– Wikipedia(Text) CC BY-SA