bhl,
if all you need is to find out is if there is an asterisk anywhere in this 50-character field, you can use the cobol verb INSPECT - syntax:
INSPECT 50-char-field-name TALLYING numeric-field-name FOR ALL '*'
if the asterisk is present, your numeric-field-name will contain a non-zero value after the statement is executed.
if you need more in terms of information, such as where the asterisk is in the field, then you can use other formats of the INSPECT verb. you can find those formats in your COBOL manuals.
hope this helps.