I'm using also Courier New by default and created a Unicode file in UltraEdit with some characters, switched to hex edit mode and replaced the code of the first character with 20 21 to get the Unicode character with hexadecimal code 0x2120. After switching back to normal text display I could see that the character was displayed as rectangular as it is typical for characters not available in a font.
So I opened Word 2007 and copied the character from UltraEdit into the Word document. Although Arial is my default in Word, Word uses font MS Mincho for the ℠ character. It could not change the font for this character to Arial or Courier New. Word ignored my font selection and uses for this character always font MS Mincho. Using font MS Mincho in UltraEdit results also in a correct display of the character. It looks like MS Mincho is also a fixed width font, but in my point of view this font is not really good for usage in a text editor.
Conclusion: I suppose this Unicode character is not available in Courier New and Arial and Visual Studio 2008 also automatically uses a different font (probably MS Mincho) for this character as MS Word 2007.
Tested with Windows XP SP3 with Office 2007 Prof. installed.
Best regards from Austria