Do you need to click the "site alias" box under TRS and then populate that list with some data in order for this to function when not set to smart zone?
Site Displ/Srch is the correct button for RSSI on a portable, press and hold to jump to another site. In my experience the numbers are in the range of 0-160, and anything better than 40-50 is normally reliable for talk out. I have never scene any tables that compare the Motorola scale to dB, dBm, etc.
With that said if the radio is only being used to scan a system then these buttons should have no function, if you can use that button and can see site data then you have affiliated and will cause harm to the radio with your fraudulent ID, and are probably commiting a criminal offense in your state. It looks like Orte is a valid system user since he depends on transmitting, but I wanted to throw that in for others using XTS as scanners.