The colon starts an announcement, introduces something, summarizes, and is always followed by more content. It indicates that this is not a one-way street, that this is not a monologue. It is an open invitation, a call for new statements, theories, questions and answers.

We place a colon after your topics: Those who use a full stop bring things to a close, batten down the hatches – the matter is finished. Period.

Certainly, now and again individual cases require a full stop or even an exclamation mark. But is PR communication not a state of permanent flux?