It's pretty straightforward: most of the time, just use your own callsign.
Because you have a U.S. license and are operating stations within the U.S., you do not need any further identification beyond your regular callsign.
It doesn't matter where you are sitting – what really matters is where the RF is being emitted.
When sharing your location with other operators, you should explicitly use the location of the station you are operating. Every station has its county, state, CQ region, ITU region, and grid square listed at the top.
For example, if you are exchanging grid squares during a VHF contest, send the grid square of the station you are connected to, not the grid square of where you, the operator, are physically located.
You may choose to add a prefix or suffix to your callsign to identify the geographic region of the station you are remotely operating, but it is not required.