Popemobile is not a proper noun. Therefore, unless popemobile begins a sentence, such as the previous sentence, it is not necessary to capitalize popemobile. Although popemobile must be capitalized, when referring to the Australian indie rock band, Popemobile.
I probably should have capitalized popemobile in this article title, but I chose not to. Yes, I used a bit of license. I wonder if one needs a specialized license to drive a popemobile. Perhaps some sort of CDL test must be passed.
Unlike popemobile, Batmobile must always be capitalized. Perhaps this is because there is only one Batman, while there have been many popes. In the US, president is capitalized when used as a title, e.g. President Clinton. Otherwise president would not be capitalized, the same logic seems to follow with pope. No matter what actor played Batman, or who drew the comic, it was still the same Batman. One Batman, one Batmobile. No other “Batmen” (I give up, should that be capitalized during speculative use), drive a Batmobile. There are not multiple Batmobiles available in different countries for Batman's use. (Though given Bruce Wayne's wealth, you would think he'd probably have a fleet of Batmobiles, but he was too busy to get caught up int he bling factor.)
Although, I'm sure Batmobile is a trademarked term in the DC Comics canon. And if DC says capital letter, then it gets a capital letter.
Now then shouldn't Green Lantern then be lower case at times. It is a title given to many different guardians of various sectors of the universe, and there have been at least 4 or 5 different Green Lanterns on Earth alone. (Amazing that Green Lanterns come in at of service, but Bruce Wayne is seemingly eternal.)
If a layman in the DC Comics universe said, “For my money Hal Jordan was the best green lantern I've seen in my lifetime,” then lowercase may appropriate, would it not?
This has gone from me just wanting to note the difference between “P” and “p”, to something so much bigger and so much more convoluted, that right now I wish I never started this stupid blog. I will never see this last hour again. Granted there was a distractdion wher I read about the Swiss Guard, the Sack of Rome, Pope John Paull II, Jan Hus, and ten othe things on Wikipedia, but alas, I've got nothing left in me for linking. You're on your own, you've got the tools. You've got the Google and the Wikipedia. You can cut and paste a few things in the search fields. There's no guarantee my links would be any better than those you'll find.