Does this help you ? It works on my machine.
DECLARE @s-2 varchar(10) = CHAR(153);
INSERT INTO Table_1 (sometext)
SELECT @s-2 UNION ALL
SELECT '1' UNION ALL
SELECT @s-2 UNION ALL
SELECT '2'
SELECT * FROM Table_1
UPDATE Table_1 SET sometext = REPLACE(sometext, @s-2, '?');
SELECT * FROM Table_1;
The first insert produces the following result:
[font="Courier New"]
sometext
™
1
™
2[/font]