For reference, I decided to use Lane Craig because he is widely cited.* And I used this article, which was recommended by a friend who like Lane Craig.
Lane Craig says this:
The sign of this sort of infinity, which is used in calculus, is ¥.At first I saw that symbol, the Y with double-strike-through, and thought, "What the hell? Is he using some obscure concept of infinity that was mentioned once by who knows which mathematician?"
I quickly found another website which used the same symbol. Apparently, the double-struck-Y was a symbol invented by John Wallis in 1655. Who also, it seems, invented the sideways-8 symbol for infinity, the lemniscus. But the website didn't explain why there were two symbols, or even seem to acknowledge it.
I could not find a single other article which mentioned the Y-with-equals-sign as a symbol for infinity. It looked pretty suspicious! And whenever I tried searching John Wallis, only the lemniscus was ever mentioned. I thought maybe the lemniscus was just so much better-known that it overran any mention of the plus-plus-Y symbol.
Eventually, with more Google, I was able to solve this mystery. It's a Symbol font problem. With certain browsers, using the Symbol font will cause the wrong symbol to appear. In particular, if you try to make the lemniscus symbol, ∞, it will appear as the Yen symbol. If your internet browser does not have this problem, I guess you've just solved the mystery of WTF Is Miller Talking About?
You learn something new every day. Sometimes things you didn't really want to learn.
*Okay, it's more like, I have had three or four independent personal experiences where someone mentioned William Lane Craig. Funny how we form impressions out of such scant evidence.