Alt Text for Pop-up Sign-up Forms

The "close" button in the top right of the Constant Contact pop-up sign-up form uses an "X" icon that has no alt text. This is a violation of web accessibility standards.

The issue should be easily fixable with a few minor changes to the JavaScript that generates the pop-up sign-up forms. It would be much appreciated if Constant Contact demonstrated its commitment to an accessible Internet by addressing this issue in a timely manner. Thank you!