Srila Visvanatha Cakravarti Thakura, in his commentary on this verse, gives the following scriptural information about the symbolic markings on the lotus feet of Krishna:

"In the following verses the Skanda Purana states the particular places on His feet where Krishna carries the mark of the flag and also other marks, and the reasons for these marks:

dakshinasya padangushtha-

mule cakram bibharty ajah

tatra bhakta-janasyari-

shad-varga-cchedanaya sah

'At the base of the large toe on His right foot, the unborn Lord carries the mark of a disc, which cuts down the six [mental] enemies of His devotees.'

madhyamanguli-mule ca

dhatte kamalam acyutah

dhyatri-citta-dvirephanam

lobhanayati-sobhanam

'At the bottom of the middle toe of that same foot Lord Acyuta has a lotus flower, which increases the greed for Him in the minds of the beelike devotees who meditate on His feet.'

kanishtha-mulato vajram

bhakta-papadri-bhedanam

parshni-madhye 'nkusam bhakta

cittebha-vasa-karinam

'At the base of His small toe is a thunderbolt, which smashes the mountains of His devotees' reactions to past sins, and in the middle of His heel is the mark of an elephant goad, which brings the elephants of His devotees' minds under control.'

bhoga-sampan-mayam dhatte

yavam angushtha-parvani

'The joint of His right large toe bears the mark of a barleycorn, representing all kinds of enjoyable opulences.'

"The Skanda Purana also states,

vajram vai dakshine parsve

ankuso vai tad-agratah

'A thunderbolt is found on the right side of His right foot, and an elephant goad below that.'

"The acaryas of the Vaishnava sampradaya explain that since the particular feet under discussion are Lord Krishna's, we should know that the thunderbolt is at the base of His small toe and the elephant goad below the thunderbolt. An elephant goad on the heel belongs rather to Lord Narayana and other vishnu-tattva expansions.

"Thus the Skanda Purana describes six marks on Krishna's right foot -- the disc, flag, lotus, thunderbolt, elephant goad and barleycorn. And the Vaishnava-toshani mentions even more marks-a vertical line beginning at the middle of His foot and continuing as far as the juncture between His big toe and second toe; an umbrella below the disc; at the base of the middle of His foot, a group of four svastikas in the four cardinal directions; at the four points where each svastika meets the next, four rose apples; and in the middle of the svastikas, an octagon. This makes eleven marks on Krishna's right foot."

Srila Visvanatha Cakravarti describes the marks on Krishna's left foot as follows: "At the base of the large toe is a conchshell with its mouth facing the toe. At the base of the middle toe are two concentric circles, representing the inner and outer sky. Below this mark is Cupid' s unstrung bow, at the base of the bow is a triangle, and surrounding the triangle is a group of four waterpots. At the base of the triangle is a half-moon with two more triangles touching its points, and below the half-moon is a fish.

"All together, then, there are nineteen distinguishing marks on the soles of Lord Krishna's lotus feet."