I am normally not around these days (Busy bee. Somebody want to see a folder dump of my archive?) but I have some information towards this marking. It is definitely not a manufacturer mark. Now it could be a sort of importer/retailer mark, however another possibility *could* be that it is a mark used by a sales union. Please jump in if I'm trailing off too far or demanding a little too much. Don't want to confoozle users, LOL!
Stuff below is "work in progress" (started 2009-June), please do NOT jump to conclusions, and let me say beforehand that the mentioned date of '1790' does not match any of the companies mentioned below.
Checking out the cover-up mark form with 'Since 1790' and 'Warranted Platinum' you can find two other marks out there which look exactly the same, except the headline. This one here reads Royal Karlsbad Society China but there also exists Royal Bohemian Fine China and (drumroll) Royal Heiden Society China. Now of course "Heiden" is not a common term or name, and in this context I bumped into two other related marks, Royal Heiden Bavaria and Crown Heiden Bavaria. Not the same mark form(s), but still a notable chip of info.
Anyway, the Royal Bohemian Fine China and Royal Heiden Society China marks are commonly found on items made by both the factory of Fischer & Mieg (est. 1803 in Pirkenhammer/Březová) and the TK Thun factory (est. 1794 in Klösterle/Kláterec). The link back to Thebrat's mark is placed by looking at his/her pattern: it's that what both Royal Heiden as well as Royal Bohemian call "Fantasy". I would say the items are vintage 1970s, based on the covered original marks (if present).
I could go on about shared patterns between Royal Heiden Bavaria / Crown Heiden Bavaria but I think that this is irrelevant here. I'll simply add mark examples for all four versions discussed:
