in sedimentary rocks
concordant with bedding planes
tend to form trails
not isolated
toe and/or heel impressions, reflecting locomotion
toes are recognizable but not sharply marked
instep shallow, rounded, not sharp
ball and heel impressions
no very fine details (unlike chiseled carvings)
consistent size and shape within one group
do not grade into something else
constant number of toes
He also provides a photo that looks rather like tennis shoe prints in
Precambrian rocks, along with discussion of why they are definitely not
footprints. I doubt that any YEC would think that antediluvian tennis
shoes are a credible explanation of the prints, so it provides a good
demonstration that footprint-like marks can be made by other means.