S3 stands for 'SpamStopper Stopper'. Spam crawlers get confused but your site visitors don't.
Spam crawlers work much like Google crawlers but they collect only a few things.
Anyone putting a naked mail address on the web today is asking for it.
Surprisingly it's easy to fool most (if not all) spam crawlers. They can't understand numeric escapes and they're not especially accomplished in reading image files - not on this level at any rate.