I'll have to admit that a "No Swimming" sign means no swimming to me. It doesn't mean no wading or walking along the sand.
I've seen "No Swimming" signs on the ocean shore due to no lifeguards or riptides or some other reason. However there are people walking along the shore wading and splashing along the water line. I've been to ponds and lakes that have "No Swimming" signs but wading and sitting on the dock dangling your feet in the water was totally allowed. Many times the "No Swimming" signs are just a CYA for the property owners.