Disclaimer: IANAL I just have strong opinions 
There are many sources on the Internet that claim that trademarks must
be adjectives, not nouns, for example
but this is contradicted by the examples shown on the very same page,
including references to trademarked names such as IBM, Google and Apple.
Names are nouns. Even a cursory look at Microsoft’s extensive (and
non-exhaustive) list of trademarks:
https://www.microsoft.com/en-us/legal/intellectualproperty/trademarks/en-us.aspx
demonstrates that trademarks may be nouns. Trademarks can be just about
anything:
- names
- words, expressions or phrases (“Just Do It!”)
- colours
- symbols
- scents
- sounds
- distinctive typographical designs, e.g. Coca-Cola
- logos
etc and I’m sure that some day some company will attempt to trademark an
emotion or frame of mind wink
Names are a definite counter-example to the claim that trademarks need
to be adjectives, and I can see no evidence that there is any
restriction on what words can be trademarked on the basis of grammatical
part of speech or lexical class.
I think the idea that trademarks must be adjectives not nouns (which as
far as I can tell is simply false) comes from the idea that the
trademark holder should not dilute a trademark by using modified
versions of it.
Using a trademarked noun like Google™ as a verb, as in to google
something using any search engine, may dilute the trademark. (I know
Google gets annoyed at people who talk about googling. I don’t know why
they don’t just trademark the verb as well, it’s not like they can’t
afford it.) Even adding a possessive “s”, as in “Microsoft’s founder
Bill Gates” or using it as a plural, as in “I bought two iPods”, might
be said by some to dilute the trademark. So pedants and lawyers trying
to justify their fees might insist on writing “Microsoft™ Corporation’s
founder” and “two iPod™ personal listening devices”.
But they still aren’t adjectives, they are proper nouns being used as
noun adjuncts.
Personally, I would be very surprised if trademark judges actually were
sufficiently silly to believe that consumers might be confused that two
iPhones are a different brand to a single iPhone just because the word
is plural, but the law often does silly things, so who knows?
Another factor may be that you can’t legally stick the trademark symbol
on something not trademarked. So if Apple wanted to use a ™ or ® on
every use of the word iPhone, they would have to forego using the word
“iPhones” unless they took out a trademark on that. So this may be a
factor too: companies too cheap to take out a trademark on the plural
but pedantic enough to insist on the full trademark treatment may be
forced into circumlocations in order to avoid the plural form, and
mistakenly think that this makes the word an adjective. It doesn’t.
A third factor may be that this is a method of distinguishing the word
from its generic sibling. If Microsoft always refers to Windows™
operating system rather than Windows, they can avoid any possible
confusion with plain old windows you look through.
Similarly, by referring to the Python™ programming language, the PSF can
avoid any confusion with either Monty Python or the snake.
But as far as I can tell, the idea that trademarks must be adjectives,
even if held by lawyers, is a myth not based on any actual restriction
on the kinds of words that can be trademarked, but is based on a
misconception of what an adjective is. The “Python” in “Python™
programming language” is still a noun.
