In my experience and discussions with those knowledgeable of family crests there are three things that might be relevant to one choosing to use a crest. 1. There is a custom in Ireland that says that anyone may use the accepted crest of their last name. Current Irish rule is that you can use the crest: "Edward MacLysaght, former Chief Herald of Ireland, in his book. Irish Families (1957) stated the position is, Arms shown in Part III, of the book, may be displayed without impropriety, of the Sept if that person really does belong to the Sept. The Clan Cian chief advises that any person desiring to bear Arms apply for a Letter of Confirmation from the Irish heraldry. See http://www.clancian-carroll.com/ 2. In America we have no noble class. Heraldry in America is a choice of each individual. One can create their own if they so desire.