Term a 'sheet something' to prove you are a published journalist/writer?

Solution 1:

The term you're looking for is tearsheet, literally a sheet (page) torn out of a newspaper; the big ones like the New York Times were called broadsheets.

Solution 2:

https://www.poynter.org/2004/your-work-as-your-best-resume-tips-on-clips/22361/

Whether you're a working reporter looking for greener pastures or a college journalist hoping for that first job, your work will always be your best resumé.

In the newspaper world, your body of work is known as your "clips," short for "clippings."

(noun) 1.1 An article cut from a newspaper or magazine
"Posters, newspaper clippings, and magazine interviews littered his walls."

^ODO

A young reporter interested in exploring new opportunities posed these questions about the process the other day: How many clips — and what kind — should I send?

An old article but still right.

Here's another one:

https://www.clippings.me/

Add your best clippings, customize your page and then share your work with the world - without a single line of code. Thousands of journalists and writers trust us with their work, and building your website takes just minutes.