Gold bills are a form of letters of credit (or bills of exchange) with a maturity of 3 months, and which can be settled in gold coins (or bullions).
Letters of credit are used since millenia. They were invented shortly after Cresus introduced the gold (or electrum) coins. Significantly, the oldest mentions of gold coins known in history are located in Anatolia (now part of Turkey) namely with Cresus and the river Pactole; and the oldest mention of letters of credit was written by Ciceron in 50 B.C. (in Epistulae ad familiares, book 3:5:4; here is one of the first translation from latin to old french, published 1542) about his travel in Laodicae, an important town in Cilicia (Anatolia).
Letters of credit have since been used in many different countries, together with the expansion of international trade. They have been widely adopted into what Adam Smith has described as being "real bills", underscoring that he has not invented them but only described in a doctrine their universal use. Fekete has demonstrated the relevance of Real Bills doctrine for an unadulterated, modern and resilient gold-based monetary system, calling them Gold Bills.
I have anticipated the increasing use of Gold Bills in international trade, replacing US dollar, writing specifically that the experience of Turkish banks in the international trade of Iranian oil during international sanctions will be a relevant knowledge.
Nowadays you can find on the largest Turkish bullion bank's web site a full range of banking services for using letters of credit in international trade :
The different types of L/C are: