Shooters Perch. Interesting...
I’ve seen those when I was at the Mandalay Bay a few weeks ago. They are very tall, reinforced solid concrete posts. I’m not sure what they were built for, maybe a sign. They have clearly been abandoned. That said, there is no easy way to ascend them without a crane, nor get down from them. Plus, a shooter should be highly noticeable up there from the venue.