contract/contract_digitized_signature/report/report_contract.xml

<?xml version="1.0" ?>
<odoo>

    <template id="report_contract_document" inherit_id="contract.report_contract_document">
        <xpath expr="//div[@id='invoice_info']" position="after">
            <div class="row">
                <div id="signature">
                    <p>
                        <strong>Customer acceptance:</strong>
                        <span t-if="o.customer_signature">
                            <img class="image" t-att-src="'data:image/png;base64,%s' % to_text(o.customer_signature)" style="border:auto;"/>
                        </span>
                    </p>
                </div>
            </div>
        </xpath>
    </template>

</odoo>