Thanks to Sean for sending that photo of a warning sign spotted along the trail north of the central Lincoln Park parking lot. We asked Seattle Parks about it, and got this explanation from spokesperson Rachel Schulkin:
People were reporting to staff that they were being stung on this trail. We put up the sign to warn people until we could investigate and decide on next steps. Today we identified and sprayed a wasp nest. Sign should be gone now.
We also only spray wasps if they are a danger to the public, as was the case here. If they are high in trees or away from heavily used areas and don’t present a danger to the public or staff, we leave them.