If the program does terminal interaction, make it output a short
notice like this when it starts in an interactive mode:
 
    <program>  Copyright (C) <year>  <name of author>
    This program comes with ABSOLUTELY NO WARRANTY (...)
    This is free software, and you are welcome to redistribute it
    under certain conditions; type `show c' for details.

#define APP_NAME "MiProgramaChulo"
#define APP_AUTHOR "Perico de los palotes"
#define APP_YEAR 2010
#define APP_VERSION "1.0.0"
 
void MostrarLicencia() //Esta función se llamaría por ejemplo al usar el parámetro "-v"
{
    printf("%s CopyRight(C) %s %s\n", APP_NAME, APP_YEAR, APP_AUTOR);
    printf("
          This program comes with ABSOLUTELY NO WARRANTY...
           blah, blah, blah ....... (resto de la licencia)\n");
}

mi_licencia = "<program> (C)opyright <author>\n This software... blah blah";
mi_licencia = str_replace(mi_licencia, "<program>", APP_NAME);
mi_licencia = str_replace(mi_licencia, "<version>", APP_VERSION);
(...)
print(mi_licencia);