Now there's an interesting question. IANAL, but here's what I understand the law to be, from years doing small business and startup stuff. It would be really nice if a lawyer or two could read through and comment....
Here's how I understand Canadian trademark law. There will be commonalities and important differences with other jurisdictions.
In Canada, one cannot trade mark an existing dictionary word. One can trademark a representation of a word. Canonical being a dictionary word, it cannot be trademarked in Canada - but particular combinations of colour, font, background, images could be trademarked.
Ubuntu is also a dictionary word - just not in an English or French dictionary, the ones best known to CIPO (Canadian Intellectual Property Office) and its associated bits of the government.
So theoretically, one cannot trademark Ubuntu, the word. There are Canadian trademarks for representations of the word, but they have nothing to do with computers and Canonical.
Having said that, "novel" combinations of ordinary dictionary words can be trademarked. I never bothered to registered "EdgeKeep" and "Securing the Edge", but I marked them as trademarks - (TM) instead of (R) - everywhere I used them. Had there ever been a dispute, precedent would have been on my side, but I could have lost to deep pockets.
For example, Office cannot be trademarked as just a word, in most jurisdictions most of the time, but Microsoft Office can be.
My understanding is that some jurisdictions limit the dictionary word restriction to specific languages, but whether this is de jure or de facto (by law or by convention), I do not know.
So this gets complicated really quickly, because ubuntu and canonical are just words, Ubuntu and Canonical refer to specific products and companies, the U&C terms may be trademarkable in some jurisdictions but not all, and, in any case...
...if one needs to refer to Canonical the company, then one may, despite that word being potentially trademarked in one or more jurisdictions. Whether one may make as liberal reference to the products of that company is another question.
But IANAL, and even if I was, it might not matter until a judge spoke on this particular question, or a relevantly similar one.
Fun, eh?
PS I really, really like the idea of using "RestrictedDerivativeBy<insertAdjectiveHere>Company" instead of Ubuntu or Canonical, because it makes the point so much better in a sarcastic and humourous way. It makes all of the above moot, but when did mootness ever stop a good debate? :->
