Please see the information below about the County’s raccoon rabies vaccination baiting program which is currently in progress. The baits may be found in the park and have been reported on some streets as well. They are not supposed to be harmful to humans or dogs, but they should not be handled and it’s recommended for dog owners keep their pets on leash during the duration of the program 
From the County Health Department Website

Over the past 19 years there has been a significant reduction in human and pet exposures to rabies throughout Allegheny County. This is largely due to the efforts of the rabies vaccination program for wild raccoons spearheaded by the United States Department of Agriculture’s Wildlife Services (USDA), who ACHD partners with for this massive effort. This year, employees and volunteers of ACHD and the USDA will be distributing vaccine-containing baits from July 31st through August 17th across Allegheny County.

The baits will be delivered both by hand from ground vehicles and by helicopter. The helicopters will be flying in North-South transects that do go over residential areas. As the transects are close together to ensure sufficient baiting, residents may see the helicopters moving slowly over the same area multiple times within a short period of time. Because this could be alarming if residents are unaware of what is happening, we ask for your help in getting the word out about the baiting and when it will be happening in an effort to minimize upsetting the public. Hand baiting will be occurring from July 31st through August 10th, and helicopter baiting will be occurring from August 10th through August 17th.

Please call the Pennsylvania Public Health Information Line at 1-877-PA HEALTH, or the Allegheny County Health Department at 1-412-350-4046 if you are exposed to the vaccine or need advice.

More information is available at https://www.alleghenycounty.us/Health-Department/Programs/Special-Initiatives/Raccoon-Rabies-Vaccination-Baiting.aspx.