Should a trademark cease and desist letter come from a lawyer or the owner of the trademark?

While usually a cease and desist letter comes from an attorney, there is no reason why it could not come directly from the trademark owner.  However, it carries more weight coming from an attorney and the attorney can varify that the usage is truly an infringment. Also, if it is sent by the owner and it turns out that a reasonable basis for doing so does not exist, the owner might be subject to a claim for an act of unfair competition.