How do you remember which rack you have left your bike in?
Use your phone to take a photo of your bike location, being sure to get some easy to find landmarks in the photo as well. E.g. if you had just taken the photo above and your bike is the front centre one, those two trees should be fairly easy to find again when you come back.

If it still takes a while to find (or the search area is very big) and your phone has GPS, you can probably tag the photo with the location as well.