My wife is 15 years with an intellectual properties law firm. I'll try to repeat this the way my non-IP brain heard her explanation. ;-)

Stormtrooper on the toy package has TM after it because that easily recognizable figure, in a setting we know to be the Star Wars universe, is trademarked. It's a notice to consumers and competitors that the entity inside the box (toy, setting, name) refers to a Star Wars franchise related item. Meaning: Consumer, - rest assured that's a real Star Wars toy. Competitors - "we'll sue if you copy it or use it without permission".

It could only have the R after it if it were an actual registered trademark granted by the U.S. Patent and Trademark Office. It isn't, nor will it ever be. Even Lucas wouldn't have tried to register Stormtrooper. He used that term, he didn't invent it. He has no rights pertaining to it unless it's being used on a Star Wars related toy, game, etc and is referring directly to that character.

He was clever with Droid because there was no known use of that shortened/slang version of Android prior to 1977. He also made his trademark application very specific and worded it to include just about every version of a personal electronic or automated device possible.