As mentioned, this portion of the Sammamish River Trail is owned and maintained by King County Parks. King County typically does a good job of proactively monitoring and cleaning up graffiti in their parks, but in case this specific case hasn't been resolved yet, it can be reported using King County Park's online citizen report tool: https://kingcounty.gov/services/parks-recreation/parks/seeclickfix.aspx.

This ticket will now be closed. Thank you for reporting this concern and improving your community!