If you have to put up a sign asking cyclists to please use your shared pedestrian path, you've designed it wrong.
As a commuter cyclist, I want to get from point A to point B as fast as I can, without dying. Just like a car driver.
When given the option of riding on the road verge, or weaving in and out of people walking their dogs with headphones on and children walking to school and friends walking along chatting to each other, and giving way to cars at every little side road, then I choose the road verge. So do people on road bikes zipping past me at >30 km/hr.
I really like the separated cycleways that Christchurch city has built. They're safe and fast and well used.
I worry about the recent proliferation instead of "shared paths" in new road developments which combine cyclists with pedestrians and discourage bikes from being on the road at all.
Shared paths are useful for children on bikes, if we teach them how to ride around pedestrians, but they're impractical for an adult cyclist trying to travel 20–30 km/hr.
Please, let's keep investing in separated cycleways for cycle commuters. That's what will get more commuters out of cars, not shared paths.