It's a FANTASTIC question.
How to read Victorian-era "anonymity underscore."
One solution - in certain situations - is to explicitly read-out the punctuation.
"In the year one eight dot dot, we ..."
"We then met a mister underscore, who said ..."
"We arrived in the village of P-underscore-farthing as the sun dimmed ..."
(Note another difficult issue is how to read-out numbers, anyway. "In the year nineteen sixty four" or "in the year nineteen hundred and sixty four" etc.)
Footnote - the only relevant answer here is Joel's. Thinking about it made me realise "blank" is a good choice. (It has a kind of Victorian sound, too.)
So, "We met mister Mac-blank..." or "In the year eighteen-blank" or "the village of p-blank-wich".
That's the best I can think of.
Spoken audio books are a huge industry, does anyone know the industry standard?