Dresden as town was the location of multiple decoration studios; no porcelain or such was actually manufactured there. Only exceptions were located OUTSIDE Dresden, like the former Villeroy & Boch factory or that one mentioned below. When seeing "Dresden" in general, always hold in mind that it was used as location of origin -or- decoration style name. Hence it can also be found used by the Dresden Pottery Co. (East Liverpool, Ohio) or the former Mueller company from Dromcollogher, Ireland. Never jump to conclusions when you see "Dresden", always verify the background. Even decorators in Dresden did not always decorate "Dresden style", many are known to have decorated items with Meissen florals (both Dresden and Meissen main decorations are florals, the school of decorating however was completely different).
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Shown mark consists of the intertwining letters 'SP', standing for
Saechsische Porzellanfabrik ("saxonian porcelain factory"); the full manufacturer name was
Saechsische Porzellanfabrik zu Potschappel von Carl Thieme. It was located in the small town of Potschappel near Dresden which was later later merged with two other suburbs, resulting in the newly-formed district of Freital (today Dresden-Freital).
Shown mark was introduced 1901 and used in that form until 1918 before it was replaced by three different successor marks. The numbers are the item number (A5497L) and various quality control numbers ("12" was the ID for the person that decorated the item in color, "50" was the ID of the person responsible for gilding).
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Note that I never comment on value, as is explained here
http://www.porcelainmarksandmore.com/resources/essay_value.php
