This is a (now obsolete) journalistic convention, to mark the end of a story. At one time, journalists had to submit their stories by telegram; they would do so and mark the end of the story by "-30-" - after which they could include personal messages to their editors, such as (humor) "I want more whiskey" or "I need money" (/humor).

Examples of these telegram-type conventions included "-20-" - more to follow, if you buy me female companionship, and "-10-" - a rumour (which often just meant, "need more money for the female companion in order to embarrass the local judge").

The previous paragraph is a lie. Actually, the "-**-" codes existed from "-10-" to "-90-", but only -30- is remembered nowadays. They existed as codes for journalists to tell editors what had to be done with the stories they filed.

It's truly a lost art.