Uncirculated coins like this one had a very special use to Callen's father.
Callen found a rare coin with Lenin's face on it among Arkady's belongings that matched coins Callen has in a box of artifacts about his past.
Hetty identified the coin as very rare because it was minted but never circulated. She mused that—allegedly—Lenin was critical of Russia in his private life. She also told Callen that apparently the coin meant something to his father. Arkady later revealed that he and Callen's father used the coins to communicate about whom they could trust.