I say approximate because several different lat-lon locations can be found here and there on the web, with two USGS locations being about 0.75 to 1.5 miles northeast of the sign.
The sign is at the junction of the Monitor Valley Road and a side road going east into Wallace Canyon in the Monitor Range.
Points on Google Earth: Geographic Center (the sign), USGS 1 (located in 1962, and USGS 2 (located in 2003); click to enlarge.
The Monitor Valley or Belmont Road cuts northeastward across the Google Earth view, with the dirt road to Wallace Canyon heading east (right) from the point marking the location of Geographic Center of Nevada sign. Highway 50 is off in the distance to the north, cutting east-west beyond low hills of the northern Monitor and Toquima Ranges.
USGS 1: the 1962 USGS point for the center of Nevada is at N39° 19' 11.7" and W116° 38' 13.3".
USGS 2: the 2003 USGS point for the center of Nevada is at N39° 19' 48.0" and W116° 37' 56.0".
The sign on the side of the Monitor Valley or Belmont Road is at N39° 18' 44.5" and W116° 38' 52.9".
The two USGS points are marked on the ground with rebar and a notice, and a point about half way in between is marked with orange cones, as shown here and here. To arrive at the site, you can drive Highway 50 east from Austin, NV, for about 26 miles, until you come to a sign for "Belmont Road." Turn right on that wide dirt road, and go south. About 14 miles of driving will bring you to the sign and the fairly main side road to Wallace Canyon. A half mile before that, a smaller dirt road cuts east toward the Monitor Range; that road will bring you closer to the actual geographic center, with the 1962 location being about half a mile east of the main road and about 500 feet north of the side road. The 2003 location is about 3900 feet northeast of that.
It was quite cold while MOH and I were there — we thought it might have been 10°F or lower about an hour earlier — and the sun was going down. We didn't try to find the actual center of Nevada; we instead took pictures of each other standing in front of the sign and called it good enough.
Geographic center of Nevada on Google Earth; click to enlarge. All three points show up as one at this scale.After getting back in the truck, we rolled north, making it to Highway 50 just as the sun was setting.
Nevada's Geographic Center at Backyard Traveler by Rich Moreno
Journey to Nevada's Center at Nevada Landmarks
The Geographic Center of Nevada at CmdrMark.com