web/web_widget_digital_signature_sale_order/views/sale_order_view.xml

<?xml version="1.0" ?>
<openerp>
	<data>

		<record id="view_order_form_signature" model="ir.ui.view">
            <field name="name">view_order_form_signature</field>
            <field name="model">sale.order</field>
            <field name="inherit_id" ref="sale.view_order_form"/>
            <field name="arch" type="xml">
            	<xpath expr="//field[@name='note']" position="after">
                    <div class="oe_clear"/>
					<label for="signature_image" class="oe_edit_only"/>
					<h2><field name="signature_image" widget="signature" width="400" height="100"/></h2>
				</xpath>
            </field>
        </record>

	</data>
</openerp>