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?
Why FCC identification rules (97.119) require only that you transmit your assigned call sign at the required intervals; nothing in Part 97 ties the call sign to the physical location of the transmitter within the US. So a US licensee controlling a US transmitter remotely, whether from the next room or across the country, simply signs with the call sign as usual. Part 97 does permit optional self-assigned indicators, but they are never required in this situation.
Watch out The state-abbreviation, district-number and ARRL-Section suffixes all echo old or foreign practice, such as the pre-1978 US requirement to sign portable in another call district, but the FCC dropped that long ago and self-assigned indicators are now purely voluntary.
Inside the US, your call sign is your call sign: remote control needs no slash anything.