This one must be a black-eyed pea.
We put this one in a less busy part of the park, so the muggle factor should not be as bad as some of our other park peas.
Some will probably spot it right off, while others will insist it is missing! I made the hint pretty specific to help those like me that tend to need the help!
UPDATE: 7/12/16 This one disappeared twice, so I relocated it to a different part of the park. Hopefully it sticks around longer.