Marks on china have not been regulated like silver marks, for instance. Each factory made up its own rules about marks used. Some used different marks for different types of ware, most changed their marks over time, often because the factory changed hands. Some also added different codes to denote each year. And early wares ofte had no marks at all!
So identifying china by its marks can be a difficult job - which is further complicated by forgeries! Marks can not be relied upon on their own; there are many other clues which help in identifying the maker and the date. These can be the colours used, the unglazed patches or rim on the bottom, the thickness of the potting or weight of the object. Another very good clue is found in the shapes used - many factories had particular shapes of vessels and designs of handles which are very distinctive.Nevertheless, it is important to have a good knowledge of marks or access to a good reference book.
There are a few basic rules which will help in determining the date of the object. The first is whether or not the word England appears at all. Up until 1891 England's china factories did not think of adding the country of manufacture, but that year the McKinley Tariff Act was passed in the USA, and after that all imports ot America had to have their country of origin on them. As English factories were by then exporting considerable amounts of china, they then placed the word England on their wares. So the first question is - does it have England on it? If so it was made after 1891. In the early 20th century factories changed this to Made in England - so if an item has this on it, it was made after the turn of the century, probably after 1910.
One problem is that so many factories did not bother to place any mark on the china at all! Very often all one finds underneath a plate or cup is a painted number, which is the pattern number, or a personal mark made by one of the workers. Up until 1870 workers were paid on the basis "good from kiln" which meant that even if you had spent hours painting an intricate pattern, if for any reason the object broke in the kiln or before it went in, you were not paid. This changed to "good from hand", a much fairer system, in 1870.
Because the workers were paid by piecework it was important that each worker's product had an identifying mark on it - I have seen tiny arrows, a particular pattern of dots, crosses etc.
The marks that the factories, when they did use them, were sometimes very specific - some factories employed "year marks" with a particular symbol to denote each year. This certainly makes dating china easier!
Another type of mark which helps in the dating is the registration mark of the patent office - not all china had these on them, but if they did it was possible to find out exactly who had registered that mark and when. The patent was valid for three years, so this helps in dating the product.