Frankly no one in the vacinity is going to see a small label on the outside anyway, if you think about it. If they're close enough to see it, it's because they're standing beside you and you're with the drone not flying. So here's what I do. I've printed out the "certificate" the FAA mails you with my number, FAA logo, etc. and folded it into a business card sized paper I keep in my wallet.
When someone approaches me and it looks like they're neutral or unfriendly about the drone, I'm ready to pull that out and flash it at them and say "I'm a registered UAV pilot by the FAA". Which is all true. "What's a UAV?" and you explain it, then follow that right up by telling them the FAA is solely responsible for the air and that I'm complying with their many rules. [Excluding no fly areas, etc. of course] They typically become friendlier at that point, it's quite disarming haha.
Another great idea and approach to the problem.
I can envision the impact your approach would have on the average Joe and Jane Q. Public who a drone pilot may encounter. I am CERTAIN that seeing the letters "FAA" followed by a set of official-looking numbers validates drone flying to a level in their eyes that mere words, alone, cannot express or transmit. Flashing an official ANYTHING has its due effects upon most people and does open many closed doors. And as you stated, EVERYTHING you say and point to via your approach is 100% legal, correct and valid, in all 50 states. Not bad. Not bad at all.