Definitely not, but it's not something you'd ever be caught for. While some states have safety inspections, mirrors aren't something they check for (other than to make sure they aren't broken), or would even think to check for. But it would technically be against the regulations for allowed equipment. I suppose it could get you in trouble if you were involved in a crash and the other side's attorney found out you had a non-approved mirror installed and this somehow might have affected the crash.