Listed in Boughey and Vickerman's 'Prehistoric Rock Art of the West Riding', no. 204. The cut and dressed stone is prism-shaped, possibly a milestone.
On its upper surface are three distinct depressions, called 'cups' in the PRAWR book, and it is listed on the Leeds UDP website under 'Class 1 Scheduled Ancient Monuments'. The Leeds City Council website lists the stone as being 440m south east of the roundabout at Horsforth on the A65. The book sites it 320m from the roundabout at Horsforth, outside house number 142. I found it to be outside this house, on a very narrow pavement. It must be a pain in the ass for folks with pushchairs!
There is a O.S. stud and benchmark present, and Boughey & Vickerman suggest the marks may actually be to support a surveying instrument.