Underline, quotation, italics?

What's wrong with it the way it is?

What.

Are you attempting to emphasize the name John? Is that the idea? Because otherwise the sentence is fine.

If you are emphasizing, use italics. Quotation marks aren't for emphasis (and a LOT of people do that and they are wrong, wrong, wrong). Quotes have purposes (quotations, titles, or to indicate skepticism on the part of the writer. There may be other usages that I've forgotten, but emphasis is not one of them). Underlining is more likely to be used to indicate titles. It can also be used for handwritten documents, simply because it's tough to get across italic versus block print when you're writing by hand. But for typewritten text, use italics for emphasis.

Why do you think any of these formatting changes are needed for the sentence?

Fellas I'm sure Rev means no special emphasis

Rev, by "emphasis," let's suppose for instance Bill refers to John as "Frank," whereupon you advise, "Bill, his name is John"