It's not an insult, though, it is a controversial topic in Serbia. Marković, a football fan, was killed a few years ago. There are, unfortunately, many similar graffiti and murals with names and images of killed fans, all over Belgrade.
There's nothing offensive on your part. You're a photographer, and, you're documenting, in this case - a graffiti! No reason to remove it, in my opinion!
I had to hurry back to the car parked almost half a klick from a beach (different from the marina above) because I had left my phone there -- my only light source. The woods sure get dark quicker than the pretty horizon of waters.
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