It's a trail on the map at the 7th Street trail head. It's a trail on maps found online. It's a trail here on HAZ.
The city plans on fixing the sign, and they can't take back what's on the net, but the route in question was not developed by the city and has a number of problems. It wanders onto and eventually ends on private property, has no signage, numerous spurs, and no switchbacks on slopes that will erode with use. The numerous crossings of small but steep washes on sometimes slippery grus actually make it fairly hazardous compared to the other trails.
That being said, the area in question is some of the most interesting in the preserve. The course grained granite of this end of the range is unique to the park. Similar in geology to Pyramid Peak to the west and the north end of the McDowell's to the east, it creates steep faces and sculpted forms not seen with the volcanic tuft and basaltic lava that makes up most of the north phoenix foothills.
There are plans to eventually improve the trail and provide a trailhead, signage, etc., but dates have not been set.
Until then, the Sonoran Preserve has 21 trails to choose from, so hikers are encouraged to hike them until the Tramonto Trail becomes what it isn't.
The closest developed trailhead is at the southwest corner of the Carefree Highway and 7th Ave, 3.1 miles west of the I-17 on the north side of Phoenix.