I've recently read the trademark policy by Ubuntu.
It mainly states that versions of the OS can be shipped by third-parties (e.g. a company) only under one of the following options:
- a commercial agreement with Canonical, or
- removing all references to Ubuntu and recompiling the packages from sources.
Since Linux Mint installs and uses the very same binary packages from the Ubuntu repository, I wonder if they have such an agreement and if the Ubuntu's trademark policy also affects the Linux Mint distribution.