MD 6: The west end seems to have been truncated to here. There was a barricade and NO TRESPASSING signs at this driveway. Signage does not show MD 6 WB going past MD 224.
Highway Location Reference describes the endpoint as "Road End: Guardrail" and it being 0.73 miles from MD 224. That quite clearly corresponds to the physical end of the road at the water. Charles County GIS also shows it being public ROW all the way to the bank of the river.
This implies the barricade and no trespassing sign you encountered may have been placed there unilaterally and unauthorizedly by one of the property owners at the end of the road. This is a thing that has been known to happen with small roads in rural areas, local property owners assert domain over them either because they legitimately think it's private and theirs, or because they just want to keep people away from their property and assume if they put up gates and signs it'll scare people off and they won't challenge it.
I'd suggest reaching out to SHA about this since if someone did put an unauthorized gate across a public road, they could have it removed.