UDI?

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Puzzle for a sunday morning. Whats UDI, whats missing?

Ok, what hints can Google give.
Unidentified Drinking Injury ? probably not.
Urban Design Institute? I don't think there's one in the picture, but I doubt its gone missing.
Unilateral Declaration of Independence? ah. But from whom, Pennsylvania ?

Ok, days over. Drop a hint.
(Is the flag back?)

The flag of the Commonwealth of Pennsylvania has been down most of this week, not back last I looked.
Sure it is just off being dry cleaned...

A .ie commenter ought to know what an UDI is without having to look it up!