Highbridge sits on a ledge above the Harlem River, and late in the day the sun comes back off the water and the old tower and lays itself across every yard on the hill. Herman Services Inc keeps those yards in shape with mowing, edging, trimming, cutting back overgrowth, seasonal cleanups and carting the waste away. Terraced ground, retaining walls, stairs where other places have driveways — nothing about this terrain is simple, and that is much of the appeal. A steep little lawn cut evenly, its border run clean along the stone, reads as an act of attention. On these blocks that reads loud.