People look at the marks on the back of china plates to identify two things: the maker and the pattern. The maker is pretty easy to determine--you usually find the name spelt out, initials or a symbol of the company. Sometimes, the pattern is easy, too, because it's clearly marked. But, other times, there's no indication of the pattern, or worse, the maker didn't give the pattern a name. Don't worry though--help is available in both those cases.
Get familiar with the field by picking up an illustrated reference book, such as "Lehner's Encyclopedia of U.S. Marks on Pottery, Porcelain & Clay" by Lois Lehner. This kind of book will give you basic knowledge and serve as a reference later.
Look at the back of a dinner plate to locate the manufacturer's mark. If it's spelt out, you're in luck. If it consists of a symbol or initials, scan appropriate books and websites to find a match and to make an identification (see Resources).
Look on the back of the plate to identify the pattern. Again, you're in luck if you find a pattern name. Sometimes, there's a pattern number; it may serve as the pattern name or lead you to the name if you search your books and other resources. For the patterns that never received a name in the first place, collectors have assigned special numbers to make your work easier.
Contact a china replacement company if there's no pattern identification mark (see Resources). Some companies encourage you to send photographs of your pattern, so staff members can help you identify it. They prefer that you photograph the front and back of the dinner plate.
Do the sleuthing yourself, comparing your pattern to those in reference books. An alternative is to subscribe to a website that specialises in identifying china marks--the cost is about £6 a month.
Appraisers and staff at speciality stores are often knowledgeable about china markings. Make an appointment and bring in a dinner plate for help with your quest.