Most couriers will not ring doorbells and this is a severe disadvantage for my wife as she is Deaf and can't here the door knocking. I installed a vibrating pager for the doorbell and most couriers wont use it.
I made a complaint to the Post Office and so far they are ringing the bell, but on occasions I have been home I still hear the door knock.
Put a sign under the doorbell is usually the best way. I may also put a sign on the door Video Surveillence installed.
