If you go through the books I read, you will find a multitude of varied marks...no real code, except may for a star by something exceptional, and I know I've told you this.
Although I didn't mark much in John McPhee's last book, Silk Parachute, each of the essays grabbed me. A reviewer wrote that McPhee can make anything interesting, and I started to disagree, seeing the essay on golf. But he did that too.
One essay was about his daughter and her photography partner who take large format photographs. Thus the title, "Under the Cloth." Anyone familiar with large format cameras will love it. Here are a few well-turned phrases I marked or underlined.. McPhee's ability to see in detail, and thus write great non-fiction:
"When they study the ground glass under the dark cloth, they are cropping the landscape rather than the picture."
"The darkly outlined final product was brightened by motion:...the ninety minute brushstroke of the moon."
"...the Deardorf spent ten evening minutes drinking in the Bridge Street bridge."
"...Laura and Virginia were drawn off the turnpike and into the kipukas of Carteret, where bungalows with picket fences survived the industrial magma."
From "Season on the Chalk," (the chalk of Europe--chalk cliffs of Dover and French champagne country) he goes into the geology of chalk embedded with flint: "Flints from English chalk ignited the powder that answered the shot heard round the world."
From "My Life List" (food he has eaten): "Sam knows the name and address of every rattlesnake in the northern five thousand acres of the island."
Of humidity in New Jersey: "You could drink the air."
Enough quotes. Other essays are about Lacrosse, fact checking at The New Yorker, high school basketball, canoeing, and New Jersey. All with well-turned phrases. Makes one want to write.