I am not certain I fully understand what you are trying to do. One thing I have done in the past with special symbols is to search out what the equivalent Code is for that character. You could then create a button that runs a script similar to:
Insert Calculated Result [Select; Char ( 9 )] // this will insert a tab character wherever the cursor is on the layout (in a field)
Insert Calculated Result [Select; TextFont ( Char ( $number ) ; "Symbol" )] // this will insert a Symbol font character of value $number
*when using the TextFont function you will want to be certain that the end-user[s] will also have this same font installed on their client-side computers.
"It is a "Pro Forma" type form which needs boxes ticked."
In filemaker, you can define a value list and apply to a text field selecting the Checkboxes option in the inspector and selecting this value list. Then you have boxes on your screen you can "tick" by clicking them with your mouse. Is this what you had in mind?