title: Is there a correct way to mask a 15 digit credit card number?
body: <p>15 digit bank card numbers are formatted 0000-000000-00000<a href="http://www.google.com/search?q=American+Express&amp;hl=en&amp;qscrl=1&amp;prmd=imvns&amp;source=lnms&amp;tbm=isch&amp;ei=hZCDTvyhCca3tgf2q7n7AQ&amp;sa=X&amp;oi=mode_link&amp;ct=mode&amp;cd=2&amp;ved=0CBgQ_AUoAQ&amp;biw=1366&amp;bih=677#hl=en&amp;qscrl=1&amp;tbm=isch&amp;sa=1&amp;q=American+Express+15+digit&amp;pbx=1&amp;oq=American+Express+15+digit&amp;aq=f&amp;aqi=g-S1&amp;aql=1&amp;gs_sm=e&amp;gs_upl=7052l8041l0l8194l9l8l0l5l5l0l114l235l2.1l3l0&amp;bav=on.2,or.r_gc.r_pw.&amp;fp=33e9e11be2878eaf&amp;biw=1366&amp;bih=677" rel="noreferrer"><sup>[1]</sup></a>.</p>
  
  <p>If I show the last 4 digits, it becomes xxxx-xxxxxx-x0000 which looks slightly goofy.</p>
  
  <p>Is there a correct way to format a masked 15 digit number?</p>
  
  <p>(I expect we will not show more than the last 4 anyway, but if there is a standard, I want to know about it.)</p>