This is the 2431st most frequent Russian word.
подписей
"Подписей" means "signatures" in English.
In this sentence, 'подписей' is the genitive plural form of 'подпись' (signature), used to indicate a quantity.
На документах было много подписей.
There were many signatures on the documents.
Here, 'подписей' is also in the genitive plural form, used to express insufficiency.
У нас не хватает подписей для петиции.
We lack enough signatures for the petition.
In this sentence, 'подписей' remains in the genitive plural, specifying a requirement.