Display control code, or non-printable character within string

I have found several records that look to contain trailing spaces after a number, but I cannot query them based on the string containing a space so I believe the records have some sort of control code or no-printable character in them.  I can select the records based on them containing something other than a number or letter, but I want to be able to see what the record really contains.  

Here is how I found the records:

select '('||month||')'
from birthdates
where nvl(length(translate(month,'a1234567890','a')),-1) > 0
/

The records returned look like this:
(1  )
(2  )
(9  )
etc.

They are not spaces that follow the numbers but I cannot find out what they are.  Basically I need to update the records to just show the month number.  The data is mostly accurate  (containing just the number with nothing following) but there are 100's that appear like the above.