The symbol on the Command key was never meant to be a computer mark at all. As the first Macintosh took shape, Steve Jobs objected to the Apple logo appearing beside every menu shortcut. Using the company's mark that often, he felt, was spending it in vain, and so the team went looking for something else to press.

The answer came from Susan Kare, the bitmap artist whose hand shaped so much of the early Mac. Paging through an international dictionary of symbols, she found a small four-lobed knot, a looped square with a loop at each corner. It had a working life already. On Nordic road signs and campground maps it marked a place of interest, a spot worth stopping for, and it is said to still stand at Swedish roadsides today, pointing travellers toward a campsite. It carried no debt to any brand, which was exactly its appeal.

In 1984 the mark shipped on the Macintosh keyboard, and it has been pressed ever since. For more than forty years it has opened and closed and copied and switched, riding at the front of ⌘C and ⌘Space and ⌘Tab, a glyph that most of the people using it have never seen anywhere else. The little knot that once meant somewhere worth visiting now means the key that gets things done, a wayfinding sign quietly repurposed into the busiest corner of the keyboard. It is a good reminder that the marks we press every day often arrived from somewhere entirely unrelated, chosen less for what they meant than for what they cost.