The ramp is Public, no problem parking in the established parking areas. As for the no fishing signs, I believe it's meant as no fishing on the ramps themselves. Not sure about under the bridge but I have seen many a person fishing there. So if it was me I'd park in the parking area, not fish on the ramps, and wander on over to the bridge and give it a shot. I would also make it a point to have a current fishing license and obey the size restrictions on any kept fish. The Warden may forgive your fishing under the bridge but he/she won't forgive an illegal fish.