Is it possible to create Ubuntu Shirts ( Merchandise )
Is it permited to use(print) Ubuntu logo on a "Ubuntu users group" T-shirt which is not sold public but to the group members ?
(I read this question.)
Your usage will be fine. Per the Trademark & copyright policy.
It's a big planet with a lot of different rules. You could probably do this legally in North Korea or a small Pacific island nation.
If you are in a country that observes and enforces international trade and copyright treaties, you need to read Canonical's Trademark and Copyright policies page. You can't use the Ubuntu name or logo without Canonical's permission for commercial use, according to the Community Advocacy paragraphs. Generally, this means that you can pass along the costs to produce the shirts, but you can't take a profit.
You should talk to a lawyer if you have a legal question. A cheaper alternative would be to just contact Canonical and ask. I've done it before and they were friendly and replied promptly. If your goal is to promote Ubuntu and just cover any costs, they can confirm that this is acceptable for you.
You can use the Ubuntu logo freely, as long as it isn't used to create a bad brand identity.
Use the Ubuntu Brand Guidelines as a guide - though make sure you don't misuse the logo as pointed out in the 'Incorrect Use' section.
Source: Ubuntu Brand Guidelines.