This isn't officially a W3 Validation service, but it does check W3 Guidelines;
You can confirm and place a recognition button of your website containing no tables.
I stumbled upon it, and it seems like a good service; You can either be confirmed Tableless to W3 Standards, allowing the occasional table in certain areas; or be 100% Tableless.
Ever wanted to see in all brilliance whether your site is tableless?
http://w3tableless.com/