Some historians, thought the discovery of a seal during excavations near dvAraka meant that it was the lost city of kriShNa, as mentioned in this article -  https://swarajyamag.com/reviews/dwaraka-history-re-incarnated

Quoting that article, “A seal of conch shell, slightly damaged and engraved with a three-headed animal motif, was recovered“, which corroborated the “statement in the Mahabharata that seals were used by the citizens of Dvaraka"+

Impossible to find the actual dvAraka, whatever they found was certainly not dvAraka. Anyway, those shlokas are from harivamSha. And no, they are not talking about an actual seal. They are spoken by bhagavAn, let me explain them here+

eka eva mahAdvAro gamanAgamane sadA |mudrayA saha gachChantu rAj~no yo gantumIpsavaH ||  

[Krishna: There is one great door for coming and going, always. Those who wish to leave dvAraka must take the “mudra” of sovereignty with them.]+

na chAmudraH praveShTavyo dvArapAlasya pashyataH |
yAvadAgamanaM  mahyaM tAvadevaM bhaviShyati

[Those without that “mudra”, will not be able to enter in the watch of the dvArapAlakAs. Until I return, this must be so.]+

Now, what is this "mudra"? The reason it is not defined by bhagavAn is because it is something very well known, ie, it is so famous that only one thing should come to mind when saying "mudra"+

“mudra” here refers to “shankha-chakra mudra” – the mark of panchasamskAra when one is branded with these marks. Just as "bhagavAn" denotes primarily vishNu, "yaH" primarily denotes Brahman in the Veda, "mudra" denotes shankha-chakra only+

This mudra is referred to as a “seal of sovereignty” by kriShNa. In the sahasranAma, he is called “svAnga” because he possesses marks of soveiregnty over all which are unique, like the shankha, chakra etc. Thus, “shankha-chakra” mudra is a seal of sovereignty+

In what way is it a seal of sovereignty? One who is branded with them is recognized as one who has no other master over him other than the Supreme Brahman. The Upanishads too say that the mukta is a sovereign as he has no master other than his natural master, bhagavAn+

The full meaning of the shloka is this – KriShNa says, “When I am gone, those who wish to leave the place of protection, dvAraka, must do so while bearing my marks of shankha-chakra...+

"...for that would show they have no master other than me, the supreme master and hence would protect them even when not in my presence or in my city. For even yama’s emissaries do not approach vaiShnavAs...”+

"...“Until the time I come back, no-one without this mudra should be allowed in the city. This is because, only in my presence, even those who lack this qualification can be purified to be my devotees, so they can come. In my absence, if you allow them, they may cause harm"+

An example of how a lack of knowledge of shAstra has impact even on historical research. If historians had more shraddha and access to traditional sources, even fields like Indology and Archaeology would reap the benefits//