I did not try this, but I believe it will work:
Create a processing rule on each report suite to prefix a fixed value (e.g. Country Code) to your country code.
This fixed value must be same on all report suites
e.g. RS1 -> Overwrite value of prop1 to concatenated value 'Country Code: '+prop1
e.g. RS2 -> Overwrite value of prop3 to concatenated value 'Country Code: '+prop3
Then you can create a generic segment:
US Segment
prop1 = "Country Code: US"
OR
prop3 = "Country Code: US"
OR
propX = "Country Code: US"
You can also add a SAINT classification on each report suite for having just the country code