It was a cast iron or steel Street Lamp post w/ silicon lamp, probably 12'-15' tall (I live in an area which uses 'vintage' street lamps).
So far as I can tell, they must have used a carbide saw or wheel to get through it, at least that was the cop's specualtion.
Why they also took the lamp post is anyone's guess, scrap value? And, if they were using a carbide saw, why didn't they just cut the chain?
After the movie, we went out and the Harley owner, his GF, and the police were there. I only told them that I saw the bike there when we went in, had to go out to my bike an hour later and the bike (and light) were gone. I didn't want to advertise my stupidity, so I left out the part about leaving my keys.
The owner was totally despondent, and the cop was saying that they'd "had a few of these in the past couple months".
I told the owner not to fret... that's what his insurance was for, that he could have the Ins. co. call me if necessary, and we left.