There is no single Unicode code for this particular character.
Unicode defines the code U+20DD COMBINING ENCLOSING CIRCLE, but most fonts (including Segoe) do not see it as a union character, but rather as its own character. For example, in Word, you will need to adjust the distance between the characters between it and the previous character (in this case U+0021 EXCLAMATION MARK) to a negative offset so that they overlap (see Using the Circle Circle Symbol in Word ).
U+20DD (. COMBINING ENCLOSING CIRCLE (U + 20DD)), (Code2000, GNU FreeFont, STIX, Symbola, XITS ..), , , , .