As indicated in a previous reply, the '?' may be the right answer - remember that the SSMS query results panel is not a text editor, and it may be limited in displaying special characters.

Apart from the other suggestions, you could write a SP that would look at all the columns you are interested and go htrough each character (RBAR-max - i.e. row-by-row, column-by-column-character-by-character ;-)) and determine which ones you don't like.

You could also use regular expressions - which would be much better and faster.

I don't have access to SQLServer right now - working on Oracle today, in which case I would use something like:

-- match only alphanumeric characters (a-z, A-Z, and 0-9)

SELECT *

FROM regex_test

WHERE REGEXP_LIKE(regex_col, '[[:alnum:]]');

untested, but I think you can do something like

SELECT *

FROM yourtable

WHERE yourcolumn NOT LIKE '[a-z]|[A-Z]|[0-9]'

B