Hi,
You can inherit the sale.order model and make necessary changes in the function has_to_be_signed .
def has_to_be_signed(self, include_draft=False):
return (self.state == 'sent' or (self.state == 'draft' and include_draft)) and not self.is_expired and self.require_signature and not self.signature
Or you can inherit the template sale.sale_order_portal_template and remove the if condition from the button.
<a t-if="sale_order.has_to_be_signed(True)" role="button" class="btn btn-primary btn-block mb8" data-toggle="modal" data-target="#modalaccept" href="#">
<i class="fa fa-check"/><t t-if="sale_order.has_to_be_paid(True)"> Sign & Pay</t><t t-else=""> Accept & Sign</t>
</a>
Thanks