I spotted this sign while driving in Chester County recently (before the winter snows set in) and had to stop and take a picture, which I did from my car window using the zoom lens on my digital camera.
The sign should say "FRESH OIL AND CHIPS." I am sure that is how it read when it was first installed. Signs bearing this warning go up on the sides of roads the streets departments have treated with a mix of crushed stone and some kind of oily substance. The treatment is supposed to help preserve the road surface, I guess, but when the treatment is fresh, it can make the road a bit slippery. Thus, the need for a warning sign.
There are two things I appreciate about the change someone made to this sign; both indicate the sign changer has a really appreciation for the nuances involved in exceptional graphic design. One, the sign editor chose a contrasting color for the "fish" edit to draw attention to the change. Two, the person chose to match the typeface used for the rest of the sign. Matching the typeface instead of, say, making the word "fish" out of hot pink fish shapes tells me the editor wanted to match the official tone of the rest of the sign while poking some fun at that same tone. Summing up, the revised design conveys a sense of gentle, tongue-in-cheek whimsy. Nice job, anonymous artist and editor!