I believe it's an anomaly in the brickwork.
I saw that also but after further study I don't think it's a part of anything he's wearing.
If you follow the line from the bend in his shoulder if follows the mortar line, as does the line below it. Plus the line above the last bend in his elbow is visible - Granted it's faint but I still see it. That would make it a very narrow protrusion with a shelf on top that happens to lineup with the brick mortar.
Lastly, there are several other anomalies in the brickwork where the mortar is very hard to see, like behind his cap and in front of his nose etc. that could explain what we're seeing.
If men are good, you don't need government; if men are evil or ambivalent, you don't dare have one.