If you were blind, you'd know why this doorknob is knurled

From the International Building Code:

26.11.4 Special hardware: Doors opening into hazardous areas shall have door-opening hardware which is knurled or has a roughened surface to give tactile warning to persons with visual impairments. Hazardous areas shall include but not be limited to loading platforms, boiler rooms, and electrical equipment rooms.

Of course then I had to look up "knurl" -

knurl:

1. A contorted knot in wood.
2. A crossgrained protuberance; a nodule; a boss or projection.
3. A lined or crossgrained pattern of ridges or indentations rolled or pressed into a part for grip.

etymology:

knur +‎ -le (“diminutive”), from Middle English knar (“knot in wood”), earlier sense “a stone”, of Unknown origin.
gnarl is a later variant, from gnarled, via knurled.

Knurl related to "gnarly."  Cool.  You learn something every day.

Image cropped for size from the original at the Mildly Interesting subreddit.