A phrase that radio stations sometimes use to lead into their top of the hour newscast.
The tone in question is usually what is technically known as a bee-doop, which is a signal from the radio network to its affiliates that something is about to happen.
In this case, the bee-doop means "the network news will begin immediately after the bee-doop." The affiliates often choose to pass that bee-doop through to the listeners, so for all intents and purposes, if they carry the network news, the news theme music begins with the tone. Even if they don't carry network news, many news and news-talk stations play a bee-doop anyway.
The best top of the hour legal ID is one with the call letters and city of license as part of a jingle, then the jingle's music bed continuing under an announcer saying "time at the tone, 12:00," immediately followed by the bee-doop, then the theme music leading into the network news.
It gets even better if the news is followed by the station going back to their music format, but music stations with top of the hour news are few and far between these days.