Checking for replication of characters in a field

To the list,
I am trying to create a utility to prevent users from entering insignificant
data in a field.  For example, if the user is required to enter a Contact
Name (which cannot be verified against any table), I can check for blanks
and issue an error.  However, if the enter a ".", "X" or all "*", an error
will not be issue. Has anyone written something like this (or similar) to
handle this?

I could write a routine to go through every character on the keyboard to
test  IF fieldname = *all'x' but what about just checking for three AAA's or
999 in a 20 character field?

TIA...
Eric Wolf