I can imagine it comes over as quite cryptic. Fortunately I know what it is about because I live near a place where that sign is also present.
First of all, I need to explain some terminology:
"Jaagpad" is a towpath; it is a road that was used in ancient times where the horses that towed the ships would walk. It is a road next to a canal or river for inland navigation (which is a transport system allowing ships and barges to use inland waterways (such as canals , rivers and lakes)). Those roads are not public domain but are owned by W & Z (see below).
"W & Z" is the abbreviation of "Waterwegen en Zeekanaal" (waterways and sea canal), and that has been renamed to "Vlaamse waterweg". It is a government institution that owns, manages and maintains the inland waterways and associated infrastructure.
Now, the sign that you saw says that access to the towpath is forbidden except (uitgezonderd) for:
- "Aangelanden": riperian owners
- "toelatingen W & Z": permit holders from W & Z
- "rijwielen": bicycles
- "bromfietsen klasse A": motorcycles class A (max. speed is 25km/h)
Hope this helps.