There's a line for a signature that the flap of the envelope ends up glued over the top of. There is no identifying information visible on the outside of a properly sealed envelope.

The envelopes have to remain sealed until they're brought into the room with the election monitors to be counted. If the seal isn't intact or the envelope isn't signed underneath or the bar code under the flap doesn't match the one on the ballot then the ballot is considered spoiled. The actual ballots are wrapped in a "secrecy sleeve" so that the votes can't be seen without unfolding them, and the election monitors separate the envelopes with the signatures from the ballots before they begin counting, so the secret ballot is preserved.

From that point forward they're processed just like any other paper ballots.