According to Ubuntu Trademark & copyright policy* their trademarks cannot be used commercially. Trademarks include words (*buntu) and logos ("circle of friends").
Removing these is good for the Trisquel identity anyways.
* http://www.ubuntu.com/aboutus/trademarkpolicy
I feel we should mark this as duplicate and you should make that point in this thread
It would be great if you could point to any Ubuntu logos that remain in Trisquel.