Return type void:
static void Main()
{
    //...
}

Return an int:
static int Main()
{
    //...
    return 0;
}

Code:
class MainReturnValTest
{
    static int Main()
    {
        //...
        return 0;
    }
}

test.bat:
rem test.bat
@echo off
MainReturnValueTest
@if "%ERRORLEVEL%" == "0" goto good

:fail
    echo Execution Failed
    echo return value = %ERRORLEVEL%
    goto end

:good
    echo Execution Succeded
    echo return value = %ERRORLEVEL%
    goto end

:end


output:
Execution Succeded 

return value = 0