Well, I sent an email to Canonical, and after a couple of days I received an answer which I place here in order to give this question as answered and to keep a record for future reference.

Hi Geppettvs

Thanks for getting in touch.

I have opened this question in AskUbuntu (How do I write articles without infringing on OSS project's logos and brands?) with no answers yet. So I found this place and dare to ask. I am the webmaster and IT consultant for several local media, radio and TV stations and newspapers at my Place in Mexico. Let's mention the TV Channel 9 (http://www.canal9tampico.com), Diario Debate (http://www.diariodebate.info), El Universo Tamaulipeco Noticias (http://eluniversotamaulipeco.com) Some of them have invited me to write a coverage or editorial column about technology and I am very interested on writing about Ubuntu and Open Source software such as The GIMP, InkScape, LibreOffice, etc. The coverage will -of course- include my personal achievements and experiences based on the day-to-day usage of these software, among other software and/or online services. I would like to know if it is legal or at least I won't break any rules by to mention the brand names, use logos to illustrate or including screenshots, video tutorials or something in the writing. I will appreciate a lot your feedback. Thanks in advance.

We are really pleased to hear your interest in writing about Ubuntu. Whilst we can appreciate the passion Ubuntu inspires, we also have to be diligent to ensure that the trademarks are used correctly.

To keep the balance between the integrity of our trademarks and the ability to customise Ubuntu, we’ve tried to define a reasonable trademark policy that allows our Community to use Ubuntu and to promote the project. You can read the full policy at http://www.ubuntu.com/aboutus/trademarkpolicy.

As you can see from our policy using the trademarks in your discussion, commentary, criticism or parody, in ways that unequivocally do not imply endorsement, is permissible. You are free to write articles, create websites, blog about, or talk about Ubuntu - as long as it's clear to everyone (including people completely unfamiliar with Ubuntu) that you are simply referring to Ubuntu and in no way speaking for Canonical or the Ubuntu project.

So as long as you do not imply that you are affiliated with Canonical or Ubuntu, please go ahead!

Good luck with your writing!

Thanks,

Isabel

After reading the Trademark Policy Document, I find quite interesting the words that refers to:

Commentary and parody

The Ubuntu trademarks are designed to cover use of a mark to imply origin or endorsement by the project. When a user downloads something called Ubuntu, they should know it comes from the Ubuntu project. This helps Ubuntu build a reputation that will not be damaged by confusion around what is, and isn't, Ubuntu. Using the trademarks in your discussion, commentary, criticism or parody, in ways that unequivocally do not imply endorsement, is permissible. Anyone is free to write articles, create websites, blog about, or talk about Ubuntu - as long as it's clear to everyone (including people completely unfamiliar with Ubuntu) that they are simply referring to Ubuntu and in no way speaking for Canonical or the Ubuntu project.

We reserve the right to review all usage within the open source community, and to object to any usage that appears to overstep the bounds of discussion and good-faith non-commercial development. In any event, once a project has left the open source project phase or otherwise become a commercial project, this policy does not authorise any use of the Trademarks in connection to that project.

Which is enough for me.