The Brasher Doubloon, the first gold coin struck in the U.S., is being offered privately at a $15 million asking price, according to numismatic adviser Jeff Sherid. His firm, Los Angeles-based PCAG Inc., is marketing the coin on behalf of a collector he would only identify as a former Wall Street executive. What is a gold coin worth today? The doubloon is dated 1787 — 11 years after the Declaration of Independence was signed, the same year the Constitution was written and five years before the federal mint opened in Philadelphia. Metalsmith Ephraim Brasher, George Washington’s next-door neighbor on New...