Unknown wires on old thermostat

[Theantiquetiger]

The thermostat I’m removing has a R wire and a G wire.  There are two wires that land on terminals that are not labeled. https://i.imgur.com/q4pnuJ7.jpeg 

[CoolingWizard]

@Theantiquetiger , you appear to have only two wire attached, both are white insulated conductors. Unless you already removed the R and the G conductors before you took the picture.   This looks like a millivolt heating system.  This type of system is not compatible with the Nest. It can be made possible with the installation of a transformer and a relay switch.

AC Cooling Wizard