Obviously, a person does not have a numerical value in their name.
That's not obvious at all. On the other hand, if it's a rule you wish to impose on your "universe", it's pretty easy to come up with a regex that will do the trick:
if (eregi( '[a-z]+', $name ))
{
// proceed as usual
}
else
{
echo "No, we don't need no ROBOTS here!"; *
exit;
}