This is the 5496th most frequent Russian word.
подписано
Signed.
Here, "подписано" is used as past passive participle indicating that the action of signing is completed.
Документ был подписан вчера.
The document was signed yesterday.
In this sentence, "подписано" describes the current state of the contract being signed by all parties.
Контракт подписан всеми сторонами.
The contract is signed by all parties.
"Подписано" refers to the completed action of the signature being added to the letter.