When planning tasks you start then according to your methodology for
workload levelling and priority but some tasks have a deadline date that
they must completed by e.g. I and others also call this a "Drop Dead Date",
though we'll use Deadline Date as its handle.

Be nice to track this and have it flagged on the gantt and other views.
I've seen this in MSP 2000 as (the head of ) a down arrow . It has no
effect on the scheduling algorithm so can easily be added. I'm suggesting
either a vertical flat head T (e.g. like a cloat if you've done roofing) or
a small hourglass or a circle with a X in it  e.g. (X) or whatever I can
layer into the canvas.

I'm doing some constraints GUI stuff so I can add this in.