Howdy -- I think this issue has come to the attention of the local authorities, as the sign at Peralta parking very clearly states that no fee is required.
There is actually legal camping in the southern lot, a few hundred neters to the south of the trailhead parking; the camping is to the SE, across from the equestrian (unlabeled) hitching post, and has several fire rings. I got there rather late, and my compadres wanted to car-camp in the uppermost parking. I went to the upper lot, set up my tent in the space by the picnic table, just south of the lot... and at 4PM, saw a "no camping" sign! It's not totally clear if that sign was just meant for the parking lot, but when the sun set at 5:30PM MST, I just sacked out... and broke camp the next morn at 4AM, never bothered by anyone.
On the way in to the Peralta trailhead, there were lots of ominous signs that discussed AZ trust land. But once we hit the Tonto national forest boundary, the attitude totally changed. As suggested above, the US marshals were probably confused, sent out to clear squatters from the AZ lands.
We had a great trip to Weaver's Needle, via Bluff Springs trail, Terrapin Trail, and a cairned use trail right to the base of the cliffs. A bit less than 7 h car-to-car, water on the way. This is the time of year to go, if you don't have to deal with ice on the route.
I have to wonder... why do we have so many Spanish place names that have "tonto"? That seems like a slightly insulting word...