I had a nasty letter at the end of last year threatening a lawsuit for an old wesbite, which may have inadvertantly infringed copyrights and trademarks. The site was old and unsucessful due to the low demand of the product and I killed it off, and it was nabbed at expiry by a third party (domain name only) Their lawyers looked for damages but were so slow it went to that third party that their case collapsed The cheeky devils tried to stop me using the product names (which are vehicles) in my metatags and pages, on existing and new wesbites. I mean, how can you have a used car website for example and not use the words "ford escort" The message here is that a wesbite should accurately describe its products regardless of trademarks etc. Thsi would be different if Nike put Adidas in their metatags, but not if you are a sports shop actually selling Nikes.
Id just ignore that to be honest with you... especially as the c&d merchants are probably US based and by the looks of things you are in zurich.... doubt they can do anything..
There have actually been a number of lawsuits over trademarks in meta tags and some have been successful and been awarded damages. "Playboy" has won a number of these lawsuits and also lost one against a former playmate who proved fair use. There is no doubt you can be sued for the use of trademarks in meta tags. Will you lose the suit? Depends on the usage. You also need to consider that it will cost thousands, likely tens of thousands, to defend your position.