When Mark S. was first hired on the severed floor, his first assignment was to refine the Allentown file. He did an unusually outstanding job, refining the file much faster than most new employees would be able to. This earned him the unique perk of a crystal cube engraved with his face, name, and the word “Allentown” which he displays on his desk.

In episode 1×02, while Irving (John Turturro) is starting to doze and hallucinate, Dylan can be heard telling Helly about Mark's “freshman fluke” that caused Lumon to overhaul the way it's Macro-Data Refinement team operated. The audio is garbled, reversed, and some words are completely unintelligible but this transcript is fairly close :

Helly: Why don’t we always finish the files.

Dylan: Cuz they only keep so long. We finish on average one in five files before they expire. Which is better than it used to be before Mark’s freshman fluke.

Helly: What’s a freshman fluke? [Reversed talk and chatter starts as Irving begins to hallucinate the black goo]

Dylan (reversed): Cuz they only keep so long.

Helly (from earlier): Oh my god, why?

Dylan (speaker side left): Now don’t go getting all impressed but I guess he was able to knock out a file of data…

Dylan (reversed): Still have no idea how he did it […]

Dylan: four out of seven of us.

Dylan: Still have no idea how he did it but they were able to reverse engineer a process based on (line levels?) […]

Dylan: Now whatever he did, now the average file takes six weeks.

Dylan: Mark still has the record which is why he has that gaudy human head.

Dan Erickson gave some explanation of Mark's crystal head award in an interview with Variety during season one:

What Erickson is referring to here might require a bit more explanation, even for the most eagle-eyed “Severance” premiere viewers who know that, yes, Mark has a glass “Mark’s Allentown” tchotchke on his desk. As Dylan (Zach Cherry) tells Helly (Britt Lower) in Episode 2, that’s not one of Lumon’s standard prizes for its Macro-Data Refiners team, it’s something Mark was awarded specifically. Later on, while Irving (John Turturro) is dozing, Dylan can be heard telling Helly about Mark’s “freshman fluke” that caused Lumon to overhaul the way it’s Macro-Data Refinement team operated.

“There’s a whole backstory there that is just kind of alluded to,” Erickson said. “But it’s basically, the idea is that Mark came in and he was inexplicably better at refining the files than others were, at least for that first file that he worked on, which was called Allentown. Each of the files has a different name and we generally went with place names, city names for the files. And so Mark came in and was able to really quickly refine this file and then they were able to reverse engineer a better procedure from what he did. We don’t get into it super far, but the idea is that he is kind of Cobel’s golden boy in that way because he came in and sort of had this great success, right when he was first there. But then it sort of tapered off since then, and people have almost forgotten about that big success that he had.”

Source: Dan Erickson interview Feb 18, 2022 - ‘Severance’ Team Answers Burning Questions From the Premiere: What Is Allentown? What’s [SPOILER] Doing? And More