Thanks for adding your support, Blasko.  If we can get a few more people to add their support, maybe Todd will take notice

Yes, I know that one.  My logo is over the top of the show in flash, so I don't need a watermark there.  Just in ssp_mobile.  that's why I'm looking for the switch.....

This could be a work around.  In your page header include this script:
<script type="text/javascript">// <![CDATA[
    if ((navigator.userAgent.indexOf('iPhone') != -1) || (navigator.userAgent.indexOf('iPod') != -1) || (navigator.userAgent.indexOf('iPad') != -1)) {
        document.location = "iphoneonlycontentpage.php";
    }
// ]]></script>

It will deliver a separate page "iphoneonlycontentpage.php" to iphones and ipads.  If you want to cover all mobile phones, get a detection script here: http://detectmobilebrowsers.com/

Once you've delivered the mobile users to a different page (or you can detect on the page and deliver a conditional set of code i.e. "this code for mobile, that code for all others") point your mobile only embed code at a different xml file path to a separate smart album that includes all the images in your original album(s).  Add the watermark to this album. 

Result:  Desktops get your traditional code and albums, mobiles get your mobile only code and smart album with watermark.