With TRUETYPEMARKERSYMBOL, the value of the character attribute is the ASCII code of the symbol's keystroke.
On Windows, you can determine the character value using the Unicode Character Map and an ASCII chart. Open the Unicode Character Map from Start > Programs > Accessories > Character Map.
The Unicode Character Map starts at character 32 (0-31 are non-printable characters). Characters 32-127 are standard ASCII codes; characters 128-255 are not standard.
For characters 32-127, use the Unicode Character Map to determine which alphanumeric key is being used for a symbol. If, for example, you want to use the question mark symbol for the ESRI Transportation & Municipal font, click the symbol on the Unicode Character Map. The keystroke box (at the bottom right of the dialog) displays the keystroke symbol (the letter "X" in this example. Now refer to an ASCII chart for the ASCII value of the letter. In this example, the ASCII code is 88 so the value of the "character" attribute is 88.
For characters 128-255, the number after "ALT+" in the keystroke window is the ASCII code.