Menu above: Edit > Settings > Profile Tab
Here you find under 'Details' the option for Country flag. You have to fill in your country code.
For a full list of country codes CLICK HERE.
To not show your flag use 'ZZ'.
If nothing is entered the 'Dynamic' flag based on your current IP address will be used.
Command line method:
To change your flag, type on the command bar under your Main Console: set fcountry XX Where XX is the country of your choise.
set fcountry US - For United States
set fcountry CA - For Canada
set fcountry ?? - (Default) resets the flag back to 'Dynamic', choosing a flag based on your current IP address.
set fcountry zz - To not show a flag.
For more information read "help fcountry".