Brought back sign reference

Author: mial-odoo

content/applications/finance/fiscal_localizations/mexico.rst

@@ -33,6 +33,14 @@ tramitesyservicios/Paginas/documentos/Anexo_20_Guia_de_llenado_CFDI.pdf>`_, a le
 of January 1, 2022. These modules also add relevant accounting reports (such as: the |DIOT|,
 enables foreign trade, and the creation of delivery guides).
 
+.. note::
+   In order to electronically sign any documents in Odoo, ensure the *Sign* application is
+   installed.
+
+.. seealso::
+   :doc:`Documentation on e-invoicing's legality and compliance in Mexico
+   <../accounting/customer_invoices/electronic_invoicing/mexico>`
+
 Configuration
 =============