Instrument not to be recorded unless date of maturity shown -- Exception

No county clerk shall record a deed or deed of trust or mortgage covering real property by which the payment of any indebtedness is secured unless the deed or deed of trust or mortgage states the date and the maturity of the obligations thereby secured which have been already issued or which are to be issued forthwith. In the case of obligations due on demand, the requirement of stating the maturity thereof shall be satisfied by stating that such obligations are "due on demand."