The 1887 has the second highest proof mintage in the series, and as the auction records indicate, proofs appear on the market with some regularity. Several very interesting proofs of this date exist. They are, in fact, mint errors, and such errors are extremely unusual in proof gold coins since those coins were generally struck with considerable care.
The 1887 three dollar gold piece errors were first struck with the reverse die aligned 180 degrees from normal and then struck again with the dies properly aligned. As a result, strong traces of the denomination and date appear upside down within the wreath on the reverse beneath the normal date and denomination. Only a few such specimens have been discovered and the first was reported and offered in Lester Merkin's November, 1965 sale.
Many proofs of 1887, and most other years as well, have a peculiar porosity in the field that can give a "halo" effect around the head of Liberty. This porosity is not an impairment and should not be confused with hairlines or rubbing.
David Akers mentioned that some of the 1887 $3 Proofs were double struck, with the second strike oriented 180 degrees from the first. Akers noted only two examples of this error but also wrote of "a few" in his book. This unusual error was first discovered in 1965 by Walter Breen.
Proof, Ultra Cameo. Double Struck, Reverse Rotated. Major Double Strike Rarity!