Os usually define every marker on every map.
Given that you have tried your best to replicate what you are describing I can see a few choices, given a bit of leeway for interpreting your replication. A single track railway line, a bridleway or a boundary marker.
The thing about walking based on OS maps is finding out if they are publuc/ permissive rights of way or for private use only. The OS maps whilst truly great guides are not definitive. The local authority usually holds, many publish on the Web, the definitive maps.