Make sure the glasses are not heavily tinted, else you'd be unidentifiable so your friends wouldn't hit you up on a conversation when they happen to walk past you.

And not to be forgotten, hearing protection.

The hard hat especially. A professor at my college died from shrapnel to the brain, and they had taken every precaution but that.

Definitely, if cutting down aluminum posts in public, the most inconspicuous thing is doing it im the daytime, wearing a hard hat, tinted saftey glasses, a high vis vest, saftey gloves etc.

Also, a portable band saw would cut through like butter compared to an angle grinder plus it's orders of magnitude quieter. I can get through 4", 3/16 drop posts in like 20 seconds with a band saw and it's much safer

Also, keep the shoe of the reciprocating saw firmly against the workpiece to start, and throughout the cut.