Full description on how SlashDot badges work is here: http://slashdot.org/faq/badges.shtml
This is the actual code that you need in your template:
I inserted my tag to appear directly below the body of my posts but you can play around with whatever position you like by using the "Preview" button. You’ll have to save the template to apply the changes when you are satisfied.
I tested the corrected code, and it’s working great!
The only probrem here is that title seems to be ignored, no idea why.
Source is correct, for some reason it is not passed to submit url page on SlashDot.