Has anyone engraved a Lower/Upper Receiver?

[Fillar]

I have too many black rifles of multiple calibers. While I know which round is for which, I’m afraid if I go visit God or I’m traveling and a family member needs to grab one quickly, a wrong round may go into the wrong receiver.

1. How do you clearly decipher between your black guns? I tend to use the same Hand Guards for caliber type, and while I have it memorized my wife and teenage won’t keep them straight; my seven year-old probably can. 
   
2. I am thinking about having 6.5 Grendel engraved on two lower receivers, or do you suggest I have the uppers engraved in case I swap lowers?
   
3. Lastly, does engraving take a finish off the receiver that can then rust?
   

I appreciate any ideas.