From the end of the 4th century the marks COMOB, CONOB appear on gold coins. OB meant Obryzum and therefore read: ''pure gold''. We also find the mark CORMOB, but all marks always end with OB. Always? No. There is a CONOR mark. At present, the numismatic community considers the presence of the letter R as a badly executed B or as a mistake. I come to show that it is a will and to try to explain this choice.