Apparently a long time ago there used to be a Forest Service road here. It has long since been abandoned, and overrun with grass. The gate is locked, and the only travel along the trail is non-motorized. So the question remains, why the stop sign? Perhaps it's because there's a possibility that someone parked perpendicular to the road in front of the gate might hit top speed of maybe 3 mph before reaching the sign? Who knows. Caution is always the utmost importance in these matters.
The cache is along side Deerfield Road in the Black Hills National Forest. There should be plenty of space to pull off the road here. It's a park and grab micro, hidden in typical fashion for this type of location. You may need an appropriate TOTT to extract the cache itself. Bring your own writing stick as it is obvious there isn't one in the container. As always, cache responsibly, CITO if needed, and have fun!