Perhaps that's debatable, but it damn sure shouldn't displayed on a cop's shirt while he's on duty, or appearing at court representing his badge.
It could be considered overtly antagonistic to a segment of the community he serves, so it would be 100% inappropriate.
Off duty, he can wear what he wants, but he's still subject to the image he projects as a police officer who is supposed to serve the entire community in which he works.
Is that a dreaded Celtic Cross for the letter "O", or is it the crosshairs of a scope? And is this cop a plainclothes detective? You've fallen for the rhetoric of the BLM.
Side with the BLM if you wish, but their goal is not the easing of racism, but the fracturing of society. They cannot be allowed to be the arbiters of what is and is not allowed unless you like the idea of quashing free speech.