[ADD] sign: document the validity of e-signatures

As requested by CJA: https://www.odoo.com/web#active_id=2227553&cids=1&id=2227553&model=project.task&menu_id=

applications.rst

@@ -18,6 +18,7 @@ Applications
    bi
    documents
    fsm
+   sign
    point_of_sale
    inventory
    manufacturing
@@ -62,6 +63,7 @@ Applications
    timesheets
    planning
    fsm
+   sign
    point_of_sale
    inventory
    manufacturing

sign.rst

@@ -0,0 +1,10 @@
+:banner: banners/sign.png
+
+====
+Sign
+====
+
+.. toctree::
+   :titlesonly:
+
+   sign/overview

sign/overview.rst

@@ -0,0 +1,8 @@
+========
+Overview
+========
+
+.. toctree::
+   :titlesonly:
+
+   overview/signature_validity

sign/overview/signature_validity.rst

@@ -0,0 +1,60 @@
+=================================
+Validity of electronic signatures
+=================================
+
+The legal validity of electronic signatures generated by Odoo depends on the legislation of your
+country. Companies doing business abroad should consider electronic signature laws of other
+countries as well.
+
+In the European Union
+=====================
+
+The `eIDAS regulation <http://data.europa.eu/eli/reg/2014/910/oj>`_ establishes the framework for
+electronic signatures in all `27 member states of the European Union
+<https://europa.eu/european-union/about-eu/countries_en>`_.
+
+It distinguishes three types of electronic signatures:
+
+#. Electronic signatures
+#. Advanced electronic signatures
+#. Qualified electronic signatures
+
+Odoo generates the first type, regular electronic signatures, and these signatures can produce legal
+effects in the EU, as the regulation states that “an electronic signature shall not be denied legal
+effect and admissibility as evidence in legal proceedings solely on the grounds that it is in an
+electronic form or that it does not meet the requirements for qualified electronic signatures.”
+
+Note that electronic signatures may not be automatically recognized as valid. You may need to bring
+supporting evidence of a signature’s validity.
+
+In the United States of America
+===============================
+
+The `ESIGN Act (Electronic Signatures in Global and National Commerce Act)
+<https://www.fdic.gov/regulations/compliance/manual/10/X-3.1.pdf>`_, at the interstate and
+international levels, and the `UETA (Uniform Electronic Transactions Act)
+<https://www.uniformlaws.org/committees/community-home/librarydocuments?communitykey=2c04b76c-2b7d-4399-977e-d5876ba7e034&tab=librarydocuments>`_,
+at the state level, provide the legal framework for electronic signatures. Note that `Illinois
+<https://www.ilga.gov/legislation/ilcs/ilcs5.asp?ActID=89&>`_ and `New York
+<https://its.ny.gov/electronic-signatures-and-records-act-esra>`_ have not adopted the UETA, but
+similar acts instead.
+
+Overall, to be recognized as valid, electronic signatures have to meet five criteria:
+
+#. A signer must show a clear intent to sign. For example, using a mouse to draw a signature can
+   show intent. The signer must also have the option to opt-out of electronically signing a
+   document.
+#. A signer must first express or imply their consent to conduct business electronically.
+#. The signature must be clearly attributed. In Odoo, metadata, such as the signer’s IP address, is
+   added to the signature, which can be used as supporting evidence.
+#. The signature must be associated with the document being signed, for example, by keeping a record
+   detailing how the signature was captured.
+#. Electronically signed documents need to be retained and available for later reference by all
+   parties involved, for example, by providing the signer either a fully-executed copy or the option
+   to download a copy.
+
+.. note::
+   The information provided here does not constitute legal advice; it is provided for general
+   informational purposes only. As laws governing electronic signatures evolve rapidly, we cannot
+   guarantee that the information is up to date. We advise you to should contact a local attorney to
+   obtain legal advice.