Whether the SteadyShot feature is turned on or not, the flashing warning icon appears when the camera chooses a shutter speed that may be too slow for the intended shot. The shutter speed chosen by the camera is in part due to the focal length of the lens and the ISO setting. It is simply an indication for you to be aware that the shutter speed being used may cause unintentional blur. This is normal operation.
If the SteadyShot feature is turned on it is possible for the camera to use slower shutter speeds than when it is off. The actual shutter speed at which the icon begins flashing, however, depends on the focal length of the lens. At short focal lengths (wide angle) the icon flashes when a relatively slow shutter speed is selected. When shooting with a long focal length (telephoto) the icon begins flashing at faster shutter speeds.
You can still take a picture even though the icon is displayed. However, since there is a chance of image blur, make sure you are holding the camera as still as possible or consider mounting the camera to a tripod.
The icon appears most often when shooting in areas that do not have sufficient lighting. Therefore, selecting a higher ISO setting or using a flash may cause the camera to choose a faster shutter speed and prevent the icon from flashing.
NOTES: The icon only flashes in the modes that automatically set the shutter speed. It does not appear when using the Shutter Priority (S) or Manual (M) mode.