AR upper marks

[Disgruntled Seabee]

I'm only asking because I don't know, what do the marks on the uppers, above the forward assist, mean? I've seen squares, triangles, arrows, many different symbols but never figured out what they mean. I've seen some people in BST put in the Ad that the AR has a certain mark, I don't believe it would raise or lower value unless it was a Colt mark maybe?
Example: the Square on this upper

 

[JustKeepSwimming]

Manufacturer ID mark. Not sure how accurate the article is being from 2012...

https://www.cdsarms.com/upper-forgings/

Square = Brass Aluminum Forging Enterprises

 

[BigWaylon]

As mentioned above, it’s the forger’s mark. There are only so many companies that actually make them, regardless of any additional engraving. Similar to AR lowers.