What is This?

[Electroenthusiast]

I'm pretty unsure to ask this ques here, but the abstract blow member lounge says : 'you can chat about anything you like', so i'm asking it here. Moreover people here might be well be acquainted with it.
Anybody here who watch old movies would be familiar with this, you can see a circular pattern in certain frames of the movie, they appear over and over again at certain times. My question is: What that circle is? Is it some watermark kind of thing? Or is something called crop circle:wiki?

Snapshot: Appears mostly at the right side of the video.

 

[dougy83]

Reel-change markers - for long movies there's multiple reels; the markings they tell the projectionist when to flip to the next reel (which is loaded on a second projector).

I saw it in action first in Inglorious Basterds - a very educational movie; not only did it teach me about the film markings, but it also taught me the history of the war.

 

[misterT]

for long movies there's multiple reels

One reel runs ~20 minutes.

 

[uthamaputiran]

misterT you are right/....

 

[Mikebits]

In the movie Fight club they called em cigarette burns.