The Apple Phone Application for Singer Enthusiasts!
It's a free app called "Singer Serial DB" (with a little black machine as the icon) it can bring up nearly every serial number out there. If it has any issues, it may also recommend an external link for more info! Not my product but it's VERY helpful on the fly, or say...in a rummage sale when you could use a little more info!
I hope this is helpful! (and not a repost)