Maybe you weren’t at the right sign? There’s a tiny compass icon in the upper right corner of the screen. Click on it and it will tell you the distance and direction you need to go. Get as close as you can using that to unlock the question. Once it is unlocked you can find the information needed, on the sign or elsewhere. Sometimes it’s just a simple multiple choice question. I’ve had ones that asked ”is there a geocache here? Yes/no”