What is this piece that looks like a coat rack or armor stand? It appears to be a coatrack or armor stand. Only marking is LEGO inside the 2 studs on the arms.  The bottom is completely blank which is uncharacteristic of a LEGO piece.  It is 3 bricks tall with 2 arms with studs at 2 bricks high and a single stud on top.  On a 2x2 base.
That would be part 4289 Boat Mast 2 x 2 x 3 Inclined with Stud on Top and Two Sides

As the name implies, it is typically use for a boat mast on modern boat models.

It only ever came in black in one set, 4669 Turbo-Charged Police Boat.