Mostly that turns on the power. Your standard Flying Brick -- strong, tough, and flying -- can easily be spotted. The speedster would need some VERY fast camera work for him to be more than blur. Teleportation requires a lot of luck to even figure it out. As for people with the power to influence people mentally, you have a nightmare of even figuring out that they did anything.
The types of powers would greatly affect the world building. But there is the flip side -- people who have superpowers who can detect the use of superpowers would also be crucial. (Protection would be even more useful, but it would need detection to be deployed properly.)