<em>*Assuming JavaScript</em>
Answer:
function send_signal() {}
send_signal() // calls the function
Explanation:
It seems that you have missed the necessary options for us to answer this question so I had to look for it. Anyway, here is the answer. The protocol that supports the encryption and decryption of e-mail messages is this: <span>Secure Multipurpose Internet Mail Extensions (S/MIME) and Pretty Good Privacy (PGP). Hope this helps.</span>
It could be interchangeable with the word program