if I etch in the word "replica" and date, someone can sandblast it right out. I'd have to etch it to 3/4 of the depth of the sign and even then someone could sandblast it and carefully metal-fill it back in. bury it for years, slap some rust on it, and no one is the wiser. so, permanent markings will not dissuade the determined counterfeiter - it just costs me time and effort. universal recognition of differences, that's the only way to go.
Sounds like you're making excuses to not even try. I have a feeling nothing anyone comes up with will be acceptable to you.
