Thank you for the post.
This was previously reported in the following thread:
In summary, this is a design change in FileMaker Pro 13. I've additionally added your research and comments to the report.
What I'm finding is that the code relates more to the UTF-16 Decimal format when you are trying to figure out what number to use rather than the Unicode value.
For example: black-right_pointing triangle is UTF-16 decimal 9654
To get FileMaker to display the WebDing equivalent of "6" the formula is Char(Code(6)+9648-48). Follow the math:
Code(6) actually returns 6+48 = 54 because Code(0) = 48 Therefore, you have to subtract 48 from what ever value you want.
The code for the right triangle is 9654. Since we started with Code(6), we have to subtract 6 from the actual value to get what we want 9654-6=9648
To make is super simple, don't even use Code in the calc. Just use Char(9654) and you'll get the exact symbol. I know it's a pain, but it does seem to work as long as you can get the decimal value for the symbol you need.