Looks like there is a way to detect if the user has run the overscan wizard and accepted a setting (either no overscan or applied one).
If you were to use this to prompt the user to adjust (and I can't find a way to launch the wizard directly) you might want to make it a one-time thing in case the user has run the wizard but decided as they didn't need to adjust anything they'd just cancel it (but at the end of the day that's down to your implementation)
String overscan = Secure.getString(this.getContentResolver(),"overscan_values");
Log.v("Overscan Setting","--"+overscan+"--");
if (overscan.equals("0.0 0.0 0.0 0.0")) {
overscan = "Overscan never run";
} else if (overscan.equals("0.000000 0.000000 0.000000 0.000000")) {
overscan = "No overscan modification";
} else {
overscan = "Overscan modification:" + overscan + ".";
}