naming conventions - Why would a JavaScript variable start with a dollar sign?

I quite often see JavaScript with variables that start with a dollar sign. When/why would you choose to prefix a variable in this way?

(I'm not asking about $('p.foo') syntax that you see in jQuery and others, but normal variables like $name and $order)

Answer

A very common use in jQuery is to distinguish jQuery objects stored in variables from other variables. For example, I would define

var $email = $("#email"); // refers to the jQuery object representation of the dom object
var email_field = $("#email").get(0); // refers to the dom object itself

I find this to be very helpful in writing jQuery code and makes it easy to see jQuery objects which have a different set of properties.