If formula on range with multiple conditions over multiple columns

I am looking to put in an if formula (or similar) in B1
The formula should give a result of Yes or No (Or True or False) or 1 or 0, the result does not really matter, it is just that it performs the check
The check should be that if all 'Trues' in the 'delivered' column, have a name recorded next to it in the Signed By column; then Yes, if not No)

So in the above table, it should show Y as there is no name recorded in B5