class ActiveStorage::Blob

def find_signed(id, record: nil, purpose: :blob_id)

The signed ID is also used to create stable URLs for the blob through the BlobsController.

that was created ahead of the upload itself on form submission.
This is particularly helpful for direct uploads where the client-side needs to refer to the blob
You can use the signed ID of a blob to refer to it on the client side without fear of tampering. 
def find_signed(id, record: nil, purpose: :blob_id)
  super(id, purpose: purpose)
end