Various assayers FM, FT, TH are reported for 1803. TH is not a match for 1802 on regal coins based on both my Calico and Cayon references. I think you have an interesting fantasy date/mint mark/assayer combination that would pass for real back in the day. These type of coins were counterfeited heavily and by many sources over the past two centuries. Starting with English counterfeits made during the Napoleonic Wars, Mexico restrikes for the China Trade, and now modern fabrications for sale to Westerners. See Swamperbob's book [Counterfeit Portrait Eight-Reales by Robert Gurney, page 363] for more. He does list an 1802 TH counterfeit with outlined eye and square base "2" in date which is what this coin appears to be. The reference number is under Class 1 [Contemporary Circulating Counterfeit], GNL#1802-O: C/R: Mo TH-001, made of debased silver alloy. The reference coin is listed as being in the Nichols Collection and was unique as of the time of printing of my edition of the book. If your coin is the next known of a Class I counterfeit, in my opinion it is worth at least as much as a regal coin. Excellent!