Wedgwood is a very complex entity, even for a seasoned collector. This short guide is purely about Jasper Ware. Modern and antique.
I'll be brief here, this is purely to aid buyers on eBay, and beginning collectors and to give a quick idea on how to tell what era a piece belongs to.
We'll work backwards!
If a piece is modern/vintage, ie: 1908-present date. Usually the marks to the reverse of any Jasper Ware piece will be Wedgwood, Made in England.
If these marks are separated, then the piece is more likely to be prior to 1970. If the stamp is all together, like so; then it is a later piece. The exceptions to the rule for this, are smaller objects, like thimbles, and other miniatures. These most often carry Wedgwood England, purely because of the size of the item in comparison to the stamp.
We can now move onto pre-1908. Items pre 1908 are marked Wedgwood England. I don't have a sample to hand for you, but it is separated, and not a uniform stamp like the one displayed above. The letters accompanying the Wedgwood England for items dating between 1891-1908 are a dating code, which I will enter into shortly.
Pre 1891, there was a three letter dating code in place. This ran from circa 1860-91. Those three letters would represent the month, the potter, and the year in that order. You can start at O for 1860, P for 1861, etc. This wasn't foolproof for dating purposes as it did overlap, and for certain letters, there are two possible dates.
Pre 1860 is Wedgwood only. Usually accompanied by other potter markings and a single letter.
I sincerely hope this helps you a little. When I have a wee bit more time, I'll come back and write something more in depth for you if wanted!
If you would like any more information about Wedgwood, and you think I might be able to help - just drop me a line. You don't have to be interested in any of my items - I'll always help if it means you can make a more informed choice when you go to make your next purchase.