I am looking at the ring and for me it looks like just a normal ring. I personally wouldn't label it as an engagement ring.
To me it looks like an engagement ring. In fact, it looks similar to my mother's engagement ring, which I am right now wearing on the middle finger of my left had as that is where it fits.
Most people I work with know I'm single so wouldn't assume I was engaged. But if people know that you have been with your boyfriend for 4 years they might see the ring, not notice which finger it's on, and make as assumption.
But yeah, it's your hand, your ring.