Some people actually only show 4 abs and have to be pretty ripped for them to show, because the abs are so large. You should be able to see something, I can see my upper abs even at 16%, but you should definately feel something if you work them at all...
In you case, the body fat was off in a negative way...can it also read to low?
Also, a better description of my abs:
When Im lieing down in my bed, and I flex my abs the appear as one bump. Starting at my obliques, you go in about 2 inches..to the abs, and then my abs slowly incline to about 1 inch higher than my obliques.. Is that normal? When I am standing straight there is not as big of a bump.