It is a simple matter to use the default dictionary to deal with this if you have material that you read frequently that uses separator lines, regardless of the character used.
I long ago added an entry to the speech dictionary to handle lines of repeated asterisks, dashes, or plus signs, when there are more than three in a row. I've extracted the component parts here:
Comment: Announce any long string of hyphens, plus signs, or asterisks as "separator line"
Replacement: Separator Line
Type: Regular Expression
If that is included in the speech dictionary any line consisting of 3 or more of those characters, in any combination, will be announced as "Separator Line." One could, of course, elect to have no replacement, but I never do that. I want to know that something has been encountered, and what the nature of it was.
I'll include a couple of examples, with a description of what follows before each. They will all read as "separator line."
All Plus Signs:
All three characters in repeating combination: