How do you know they didn't intend to enter a smiley face?

Because he never gets smiley faces from them. Of course, he gets a suspicious number of Js.

Well, there have been people whose emails would consistently end in a J on a single line. And these aren't people that would end their mails with a single smiley on the last line. Some of them probably don't even know what a smiley is.

...do their names start with 'J'?

J