What punctuation mark states that more is to come?

The only punctuation mark that may do this is the ellipsis. Sometimes writers use an ellipsis to indicate that someone is trailing off.

Typically, the ellipsis is used to show that text has been omitted from the sentence or document, but stylistically, an ellipsis may get the job done if you're looking to show "more is to come."

A colon is the only punctuation mark that indicates that more information is to come. An ellipsis, which is used when you are quoting from another written source, indicates that something has been omitted: that is what the Word 'ellipsis' means. Any other use of it is at best colloquial and at worst incorrect, and should be kept out of formal writing.