A trumpetter and a statue?

[ValentinianVictrix]

That is part of the Cornu, it is a strengthening bar. Look at my avatar, and you will see what I mean.

That bar has two main purposes. To strengthen the instrument, and prevent it from breaking, especially when made of brass rather than bronze. Also for ease of playing, that bar rests on the left shoulder so the instrument is relatively comfortable to control, especially whilst on the march.

Have a look again at the picture you posted, on the figure on the rights left arm there is a very solid looking object which is most shield like in appearance. Its nto the strengthening bar, as you can clearly see that as well. Its something solid and shield like on his arm.