AIG Ins. refusing to honor the Rider to my Ins. Policy. They had me sign a faxed document (and faxed back) acknowledging something that was only made reference to by page and paragraph #. In other words, I signed something that did not state its purpose or legal implication/information. Also, is a faxed document a legal document? They have no original signature.
Many many thanks!

First of all, I won't say something like: "Why in the world would you sign something
without knowing exactly what it referred to." It would be rude to say that.:(

So, in answer to your question, your signature on a fax is legally binding.

" An electronic signature is any legally recognised electronic means that indicates that a person adopts the contents of an electronic message.[1] It may be an electronic transmission of the document which contains the signature, as in the case of facsimile transmissions, or it may be encoded message, such as telegraphy using morse code. Increasingly, encrypted digital signatures are used in e-commerce and in regulatory filings as digital signatures are more secure than a simple generic electronic signature.[2][3][4] The concept itself is not new, with common law jurisdictions having recognized telegraph signatures as far back as the mid-19th century and faxed signatures since the 1980s.

In many countries, including the United States, the European Union and Australia, electronic signatures (when recognised under the law of each jurisdiction) have the same legal consequences as the more traditional forms of executing of documents."

Here is the reference for the above information:

Electronic signature - Wikipedia, the free encyclopedia