No fix (and a "?" too) was shown when the GPS is not connected.
I remembered I read an ESRI tech document saying GIS Mobile would work with any GPS supporting NMEA .
With that saying, it means it use NMEA protocol to talk with GPS. So you will have to use NMEA (another option is "Auto" in GIS Mobile).
In GIS Mobile, the first screen after you open a mobile project, click on Memu and then "Settings..." Then you see "GPS GPS Setting..."
In the next screen, click on "GPS Connection Setting if you want to make changes. It is where you can change the GPS setting.