web_digital_sign/views/we_digital_sign_view.xml

<openerp>
    <data>
        <template id="sale_order_backend" name="sale_order assets" inherit_id="web.assets_backend">
            <xpath expr="." position="inside">
                <link rel="stylesheet" href="/web_digital_sign/static/src/css/digital.css"/>
                <script type="text/javascript" src="/web_digital_sign/static/lib/jSignatureCustom.js"></script>
                <script type="text/javascript" src="/web_digital_sign/static/src/js/digital_sign.js"></script>
            </xpath>
        </template>
    </data>
</openerp>