What indicator is required to be used by US-licensed operators when operating a station via remote control and the remote transmitter is located in the US?

Under FCC Part 97 rules, when a US-licensed amateur operates a station via remote control and the remote transmitter is located within the United States, they are simply required to identify with their assigned call sign. There is no regulatory requirement to append any special indicator, such as "/R", a district number, or a state abbreviation, to denote that the operation is remote. The station is identified exactly as if the operator were sitting at the physical transmitter site. While some operators may voluntarily add modifiers to clarify their operating location for the benefit of awards or contests, the FCC mandates absolutely no additional indicators for domestic remote control operation.