I'm the same as Jemma, I had a listing deactivated and an email from LEGO. You absolutely HAVE to have this disclaimer in any listing that has Lego items in it:
"LEGO®, the LEGO logo, DUPLO®, BIONICLE®, MINDSTORMS®, the BELVILLE, KNIGHTS’ KINGDOM and EXO-FORCE logos, the Brick and Knob configurations and the Minifigure are trademarks of the LEGO Group of companies, which does not sponsor, authorize or endorse this site."
And this is also from the email: "There are a few problems with your listing, but the good news is that they’re all easy to fix. First, your title, “Lego Christmas Tree cards”, shouldn’t contain the LEGO term, as it’s a trademark owned by the LEGO Group. You may use a generic term instead of the LEGO word mark (i.e. “Building Block Christmas Tree Cards”), but be careful not to use another person or company’s trademark."
The lawyer was actually really helpful and nice :)