Insert/Use Registered Trademark Symbol

import from Illustrator hasn't allowed me to extrude for 3D purposes

right click on the illustrator layer and choose -> create shapes from vector layer. shapes will allow you, under the Ray-Trace/Cinema4D renderer, to extrude.

I couldn't find Glyphs in AE

none available yet

you can just copy paste the glyph from the web to a text layer. here it is:

®

Text layers and Shape layers are the only layers that allow extrusion in Ae.

BTW if you want to create it by yourself just type the letter R, and for the circle create a shape with just a stroke. you can customize the shape when you twirl down its content menu

or highlight the shape layer and when selecting the paremetric shape tools or the pen tool you can customize it in the fill/stroke options in the tools menu