What izz-zit?

I'd just say record says rebar but found iron bar in substantial agreement, accepting...

It sure looks like an axle to me.  In my neck of the woods, anything at a corner especially if it fits is surprisingly awesome.  I wouldn't even blink it it was something other than what was called for, wouldn't have thought to blink.

We find a lot where the plat or Record of Survey was recorded before the pins were set, when we find a pin that's almost exactly an even foot off, was it possibly a witness or a bad set? In your case the plat was possibly recorded with all being bar & cap, but they found the bar you did and didn't file an amended plat.

We don't record until the crew sets pins, so we can reflect what they actually did and why.

Obviously someone must have found it in the past, that flagging looks pretty old.  It almost looks like pipe set over a rod and then fused by the time spent in harsh soils.  For that matter, the flagging almost appears to be imbedded as well.

Looks like a No.5 to me with a bunch of stuff attached to it. It might be in a pipe, a good wire brushing may reveal more information. 

If you took a wire brush to it with something acid like vinegar, you might get a better idea. I've seen some oddities set where rebar were called for, I suspect because the field crew ran short on pins and didn't want to have to return, so improvised. Almost looks chiseled.

It may be one of those No5 rebars with a pointed end that has been driven butt end first. The point has been blunted in consequence.  

Deadman anchor.

Tough one, but I think like the others who think it's a fused bar, and pipe. Good luck with your investigation.

Could be the input shaft of a manual transmission.

The input shaft has a splined body which goes through a collar on the clutch disk. The collar has matching splines that transmit torque from the engine when the clutch is engaged. At the tip of the splined portion of the shaft there's a small round piece that rides in a pilot bushing in the engine flywheel. The shaft tip and the pilot bushing keep the input shaft aligned.

The input shaft generally has a gear on the other end, depending on what kind of vehicle it came from. If that's the case here, the gear might be 8" or 10" below ground.

To me it looks like an axle or a pipe with a PK nail driven in the top of it

IPF..............

I’d not accept it as anything until I had CONFIRMATION that there was no rebar nearby. 

To me it looks like a castle nut on the end of a threaded axle with flagging under the nut. 

Is that just a dark spot on the rusted surface or is it crud filling an eye at the end of the rod?

Sounds like a road trip. The first annual "RPLS-What is it?" meet up. Then we can lay the  "WHat is it" speculation to rest, once and for  all. 

All great answers from various walks of surveying experience.

My experience says this is a certainly a no. 5 rebar that has been withered over time and it is left just like this.

I have seen plenty in my life just like so; this is my final answer.