I have mine engraved only on the flat flange at the rear of the receiver. Many builders mark them there, and I've never, ever heard of improperly located markings. Orion is being overly cautious on the whole "conspicuously marked" clause which is why I personally would never use them. As long as it can be made visible without the use of any tools whatsoever, it is acceptable. If it literally had to be 100% visible 100% of the time, then the markings on the top spine of the receiver would be illegal, as they are covered up when a scope mount is installed. And even then, some of them require tools to remove, and it's still not a problem. If it can be easily identified upon inspection, it's fine.