lucy24 - 11:26 am on Jun 17, 2012 (gmt 0)
They're trying to scare you. A lawyer cannot unilaterally declare that you are infringing a trademark; that's for a judge to decide. The lawyer is gambling that you do not know this.
Did they bother to mention what the supposedly infringed trademark is? If you are in the US, the USPTO has a nice website with search functions intended for humans (that is, as opposed to patent attorneys). You can look up the trademark.