Back in my university days, the track on campus used to have explicit signs for at least two things - 1) Slower walkers/runners keep to the outside lanes and 2) Don't use lane 1 if you're not on the track team (or something to that effect).
Rule 1 should be somewhat obvious to anyone who uses a highway/freeway. It's simple consideration. The faster runners are probably timing their laps. If you're walking, it's best not to get in their ways. However, sadly, I do see a lot of folks that don't seem to care, more so on the track than the highway. People walking in lane 1 while chatting with their partner or on the cellphone. (Similar to a highway sometimes, isn't it?)
The campus folks were pretty good, even stringent at times, in enforcing rule 2 to the extent that they would block lane 1 altogether by putting up hurdles all around. After talking to some knowledgeable folks, I found the reason for doing so was to prevent wear and tear. Apparently, it is pretty expensive to lay out a track like that (upwards of $100,000) and the lifespan is less than 10 years. So, the idea was to make it last longer. Apparently, lane 1 is the most vulnerable. I guess this would be something like a carpet which starts to wear first from the edges.
Other than that campus, I've rarely seen any such signs on high school tracks. I wonder if it is because 1) they don't know, 2) they don't care, or 3) the lane 1 wear concept is a myth. I'm inclined to think it is 1.