I'm not sure I understand what counts as a sigil and what doesn't. How many sigils does the following line have?
> echo $foo # $foo refers to the contents of the variable foo
> echo $foo # $foo refers to the contents of the variable foo
* a non-alphabetic character
* that is at the start of a word
* that communicates meta-information about the word.
He gives the example of `echo $USER`, where `$` is a single that communicates that `USER` is a variable, presumably with some contents. Thus, I'd wager `$` is a sigil in `$foo`.