I bought this maybe 20 years ago without knowing much about trade dollars, paid maybe $60. Wanting to sell it now. With 7 power, I cannot detect any mint mark above the D, but still not sure this is a proof coin with circulation. Is it common for this coin to have the S removed and still not be able to detect it with 7 power?
I'm 99.99% sure it's not real. No business strike coins were made in Philadelphia in 1878 and yours most certainly isn't a proof. It has the appearance of a classic Chinese fake: - Looks like a business strike in a year where there were none - Mushy details - Strange color
Definitely fake, but @-jeffB has an interesting story regarding an 1878 trade dollar with no mintmark...