Depending on what the encoding of your input and your script is, you cannot easily use a literal multiplication symbol without decoding your input.

Personally, I would always use the named UTF-8 characters:

s/\N{MULTIPLICATION SIGN}//g;
[download]

Especially if you pull in user input from a HTML form, you should use Encode to decode the input from the character set that your user sends you, and encode the output again when you inline it into your HTML.