A circle/donut shape means they are fertilized. A dot means they are not. I don't really tell people they are fertile, unless they ask. Not that I am trying to hide the fact, but I just simply don't think about it! And, there is no difference in taste or anything anyway. I used to think, many years ago, that eating fertile eggs was just gross, but that's before I had my own poultry, and I learned what exactly that meant.
And, yes incubation is what starts the eggs' development. I have had people ask me that, too, as if they are going to crack open an egg to find a baby chick peeking out at them. By refrigerating them, you destroy the chance of it developing further. Where you could run into trouble is if you find an egg which a hen has been incubating for a few days. Eww! So, if you collect daily, you won't have this problem.