Have you even need to insert a special symbol into the document? I think, yes. But had you such possibility to make it easy? I think, no.
Now doing it is very easy with help of CKEditor & TinyMCE Special Symbols plugin.
Now you can:
Insert any unicode special symbol of range of codes set in the config
Use dropdown popup or dialog for it
Insert special symbol as an image with specified font and size (this is optional)