What do the organic symbols mean?

Could you please tell me the differences betwen the organic symbols? The only organic foods I will purchase are those with the Soil Association logo as i feel that product is top quality. The other logos I have read allow a certain amount of non-organic constituents/ingrediants (??up to 30%) in their products, i.e. Tesco I have heard are bad for doing this.I feel also using this '30%' rule (if it is true) is just to allow supermarkets to make more of a profit from those of us who prefer organic foods.
Could you also tell me why the Soil Association logo isn't displayed on your site?
I was looking under Derbyshire for organic producers. I use one in the village of Hognaston near Ashbourne Derbyshire which is Soil Association approved but not mentioned on your site. This is the first time i have used this site and i wish i had done so before! It is excellent. I am now making more of an effort to access local organic produce as i have always fed my children 100% organic food. I am just wanting confirmation really about the logos and labels because of the fear of having non organic produce put in when i believe it to be the real thing.
Can i just also say how the organisation of organics is a difficult one to access as i am so upset to believe something is organic but the animal (for example) has been given a diet of non organic feed or antibiotics or chickens have been described as organic but they are given a diet of 20% non organic food and 80% organic. It is this kind of situation whaich makes me very mad!! Which is where the soil association (i think!!) asks for stringent standards, of organic farming 7 years pesticide free soil, etc etc.
Thanks for reading this and I hope i have put my fears down in a way you totally understand!
Best wishes
Deborah Morgan-Graham