I think I heard it in the context of slacking off on work.
I know it from Underworld’s techno classic “Born Slippy”, from the Trainspotting soundtrack.
I'll put a joke here so you can skip it if you want to.
Long, long ago there was an Indian tribe with a princess being courted by two braves, Running Bear and Falling Rocks. They both had their good points and their bad points so the princess could not make up her mind which of the two she preferred. After all too much dithering around her father called the two of them in and said, “Look, we’ve got to settle this. My daughter loves furs. You two go out and whoever returns before the next full moon with the most good-quality furs shall have her hand in marriage.”
The two of them took off and a day before the full moon, Running Bear returned staggering under the weight of the furs he had collected. “Wow! Falling Rocks is really going to have to outdo himself to beat this!” The day passed, the moon was full, but Falling Rocks did not return. They waited an additional week to be fair but he still did not show. Running Bear and the princess married and had a reasonably happy life but the tribe was concerned about its missing member.
Search parties were sent out to all points of the compass but did not find him even after years of looking. They eventually stopped searching but never gave up hope. Even today, generations later, you can see the signs they have put up, WATCH FOR FALLING ROCKS
A friend of mine once pointed to a WATCH FOR CARS sign and said, “boy, they’re offering a really bad trade”.
Not from Pittsburgh, AFAIK.
Not really, but now I wonder if “slippy” means the same in Pittsburgh and Cardiff…
OK, I don’t get what’s funny about that one, either.
There is an old, faded advertisement in a small Ontario sign for SOPE. I chuckled slightly the first time I saw it, I guess.
Anywhere a country road is hilly and curvy you’ll often see it slipping between earthen cuts or banks. Usually preceded by signs saying “DO NOT PASS”.
I used to comment that the famed Colonel DoNot who surveyed most of the hilly and mountainous western USA back in the 1870s-ish sure liked to name passes after himself. “Wow, dear, there’s another one. Ol’ Col. DoNot sure got around!!” 
I sometimes get phone calls from one of the colonel’s underlings. Some grunt named PRIVATE CALLER.
A local cafe had a neon sign indicating “OPEN DAY & NIGHT”. A couple of letters burnt out leaving “OPEN DA NIGHT”.
Since then, it’s often referred to as “Open Da Night”, and all the locals know what you mean if you ask for directions.
I’ve been a member here going on 17 years and lurking for longer than that.
Yeah there isn’t jack you can do about falling rocks. Well I guess you could try to be ready to evade if one falls in front of you.
It’s really about ‘fallen’ rocks. Quite common in the spring in the Rockies.
My Uncle had a joke. ‘Falling Rocks’ was and Indian boy that got lost long ago. No one could find him. So signs where put up to look for him.
I worked for a time in Stoke on Trent, then the centre of ceramics and potteries, which had many specialised jobs and job titles, such as putting the handles on cups*. In those you could advertise jobs for a specified gender. My father, when he visited, was much taken with adverts like “Female Handlers Wanted”.
- There was also a job of “Saggarmakers’ Bottom Knocker”, but that’s another story.
Jean Stapleton told a story about seeing a newspaper ad that said “Polish men wanted” and wondered why a company would want workers of a particular nationality. She then saw it was a shop that was looking for men to do polishing work.
Just yesterday I was at an event and part of it was watching a pod-cast live. A guy told a story, and part of it was about finding a Rolex while riding his bike and trading it for a Porsche 914.
The main point of the story was about Paul Newman’s Rolex Daytona that he sold at auction for over $17 million.
Yup, that’s why I knew that @EinsteinsHund was referring to you!
Longevity has its privileges.