Gustav Thurnauer opened a store in New York City in 1883, selling high quality kitchen items -- many from Germany -- and focused on well made gadgets and porcelain items and everything kitchen.
This little egg cup is one of those pieces. It is in beautiful condition. No chips or cracks, the ducks and clovers have all their details. It has two finger grips and is marked 3997 on the bottom. Most likely a pattern number.