There are certain particular marks on the feet of the Lord which distinguish the Lord from others. The marks of a flag, thunderbolt, and instrument to drive an elephant, umbrella, lotus, disc, etc., are on the bottom of the Lord's feet. These marks are impressed upon the soft dust of the land where the Lord traverses. The land of Hastināpura was thus marked while Lord Śrī Kṛṣṇa was there with the Pāṇḍavas, and the kingdom of the Pāṇḍavas thus flourished by such auspicious signs. Kuntīdevī pointed out these distinguished features and was afraid of ill luck in the absence of the Lord.
(Srimad Bhagavatam------1:8:39------purport).

The beauty and opulence of the world can be enhanced by the grace of the Lord and not by any man-made planning. When the Lord Śrī Kṛṣṇa was present on this earth, the impressions ofthe special signs of His lotus feet were stamped on the dust, and as a result of this specific grace, the whole earth was made as perfect as possible. In other words, the rivers, the seas, the forests, the hills and the mines, which are the supplying agents for the necessities of men and animals, were fully discharging their respective duties. Therefore the riches of the world surpassed all the riches of all other planets in the three planetary systems of the universe. One should, therefore, ask that the grace of the Lord always be present on earth so that we may be favored with His causeless mercy and be happy, having all necessities of life. One may ask how we can detain the Supreme Lord on this earth after His mission is fulfilled and He has left this earth for His own abode. The answer is that there is no need to detain the Lord. The Lord, being omnipresent, can be present with us if we want Him at all. By His omnipresence, He can always be with us if we are attached to His devotional service by hearing, chanting, remembering, etc.
(Srimad Bhagavatam------1:16:32-33------purport).

The soles of the Lord's lotus feet are marked with śaṅkha-cakra-gadā-padma—conchshell, disc, club and lotus—and also by a flag and a thunderbolt. When Kṛṣṇa walks on this earth or in the heavenly planets, these marks are visible wherever He goes. Vṛndāvana-dhāma is a transcendental place because of Kṛṣṇa's walking on this land frequently. The inhabitants of Vṛndāvana were fortunate to see these marks here and there. When Akrūra went to Vṛndāvana to take Kṛṣṇa and Balarāma away to the festival arranged by Kaṁsa, upon seeing the marks of the Lord's lotus feet on the ground of Vṛndāvana, he fell down and began to groan. These marks are visible to devotees who receive the causeless mercy of the Supreme Personality of Godhead (tavānukampitām). The demigods were jubilant not only because the appearance of the Supreme Lord would do away with the burdensome demons, but also because they would be able to see upon the ground the transcendental marks from the soles of the Lord's lotus feet. The gopīs always thought of the Lord's lotus feet when He was walking in the pasturing grounds, and, as described in the previous verse, simply by thinking of the Lord's lotus feet, the gopīs were fully absorbed in transcendence (āviṣṭa-cetā na bhavāya kalpate). Like the gopīs, one who is always absorbed in thought of the Lord is beyond the material platform and will not remain in this material world. It is our duty, therefore, always to hear, chant and think about the Lord's lotus feet, as actually done by Vaiṣṇavas who have decided to live in Vṛndāvana always and think of the Lord's lotus feet twenty-four hours a day.
(Srimad Bhagavatam------10:2:38------purport).

Akrūra then saw Kṛṣṇa and Balarāma in the village of Vraja, going to milk the cows. Kṛṣṇa wore yellow garments, Balarāma blue, and Their eyes resembled autumnal lotuses. One of those two mighty-armed youths, the shelters of the goddess of fortune, had a dark-blue complexion, and the other's was white. With Their fine-featured faces They were the most beautiful of all persons. As They walked with the gait of young elephants, glancing about with compassionate smiles, Those two exalted personalities beautified the cow pasture with the impressions of Their feet, which bore the marks of the flag, lightning bolt, elephant goad and lotus. The two Lords, whose pastimes are most magnanimous and attractive, were ornamented with jeweled necklaces and flower garlands, anointed with auspicious, fragrant substances, freshly bathed, and dressed in spotless raiment. They were the primeval Supreme Personalities, the masters and original causes of the universes, who had for the welfare of the earth now descended in Their distinct forms of Keśava and Balarāma. O King Parīkṣit, They resembled two gold-bedecked mountains, one of emerald and the other of silver, as with Their effulgence They dispelled the sky's darkness in all directions.
(Srimad Bhagavatam------10:38:28-33-------translation).

"Those things which awaken ecstatic love are called uddīpana. Mainly this awakening is made possible by the qualities and activities of Kṛṣṇa, as well as by His mode of decoration and the way His hair is arranged." (B.r.s. 2.1.301) The Bhakti-rasāmṛta-sindhu (2.1.302) also gives the following further examples of uddīpana:
smitāṅga-saurabhe vaṁśa-śṛṅga-nūpura-kambavaḥ
padāṅka-kṣetra-tulasī-bhakta-tad-vāsarādayaḥ
"Kṛṣṇa's smile, the fragrance of His transcendental body, His flute, bugle, ankle bells and conchshell, the marks on His feet, His place of residence, His favorite plant (tulasī), His devotees, and the observance of fasts and vows connected to His devotion all awaken the symptoms of ecstatic love."
(Sri Caitanya Caritamrta------2:23:51------purport).

It is stated in Śrīmad-Bhāgavatam that when Akrūra, who drove Kṛṣṇa from Vṛndāvana to Mathurā, saw the footprints of Kṛṣṇa on the land of Vṛndāvana, his ecstatic love for Kṛṣṇa increased so much that the hairs on his body stood up. His eyes became overflooded with tears, and in such ecstasy he jumped out of the chariot and fell down on the ground and began to chant, "How wonderful this is! How wonderful this is!"
Similar feelings were expressed by the gopīs when they were going to the bank of the Yamunā and saw Kṛṣṇa's footprints in the dust. When Kṛṣṇa walked on the ground of Vṛndāvana, themarks of His sole (flag, thunderbolt, fish, a rod for controlling elephants, and a lotus flower) would be imprinted upon the dust of the land. The gopīs became overwhelmed simply at seeing those marks on the ground.
(Nectar of Devotion).

All the gopīs were madly feeling the absence of Kṛṣṇa. They inquired about Him from the trees and plants. In some places they found the imprints of the marks on the soles of His feet—namely the flag, the lotus flower, the trident, the thunderbolt, etc. After seeing those footprints, they exclaimed, "Oh, here is the impression of the marks on the soles of Kṛṣṇa's feet! All the marks, such as the flag, the lotus flower, the trident and the thunderbolt, are distinctly visible here." They began to follow the footprints, and shortly they saw another set of footprints beside them, and immediately they became very sorry. “Dear friends, just see! Whose are these other footprints? They are beside the footprints of the son of Mahārāja Nanda. It is certainly Kṛṣṇa passing through, resting His hand on some other gopī, exactly as an elephant goes side by side with his beloved mate. We must, therefore, understand that this particular gopī served Kṛṣṇa with greater affectionate love than ourselves.
(Krsna Book).