People stop me all the time and ask "what's the best way to find a ghost sign?". Then they usually follow up by asking if I have spare change.
1. Look up. There are very few ghost signs painted on the ground.
2. Go where you don't usually go.
3. Go when you don't usually go.
This big, obvious Powell Valves sign on Colerain in Camp Washington was invisible to me for a long time, because it faces north, and I'm usually looking at things from the south. And there were trees making it more difficult to see from the street.
4. No. None of my change is spare.