Greetings! There are two ways to insert special ASCII characters into a text block. In the text block toolbar, you can click on the icon for Insert and scroll down to Special Characters. A window will open over your main editor screen where you can select the character you need.
If course, if you are comfortable editing the HTML code (it's really not difficult), you can switch to Code view.
A new edit window will open showing the HTML code for the text block. You can then add the HTML code for the special character you wish to use -- use ® for the registered trade mark sign, or ™ for the trademark sign.