I ran into these signs along a city park trail and initially worried about the mention of USACE:
The first sign makes no mention of ownership. However, the second clearly sates "...owned by the City of..." I also searched the Facility List for Recreation.gov and found no mention of the park name. Since it is not CoE land, no longer a concen.
Unless I missed it, the wooden sign is all that is visible if you approach from the east [with multiple postings of the metal sign from the west.] With only the information on the wooden sign, it reads to me like a possibility of the land being CoE and off limits. No official looking USACE sign with the castles on it though. Would anyone else give the pictured wooden sign a second thought if you came across it unexpectedly?