The messaging application Signal has gained a large number of new users due to his recent "scandal" WhatsApp, who announced that he would share the data of users to Facebook, due to some changes in its policy.

However, after that, people are extremely skeptical about how others use their personal information applications, such as Signal.
Signal only seems to be asking for it Telephone Number and does not try to track users while you can use it even though do not give it to him access in your "Contacts".
However, although it is considered one of the safest applications, there is a case to send messages that are not completely secure.
How to check if the messages you send are not secure?

In general, Signal offers end-to-end encryption, which means that only the sender and the recipient can have access in the messages. However, this may not be the case if you have set Signal as the default SMS application in Android. In this case, you can see if the messages are not secure in the following way:
- The send button will be gray and will have one small icon with an open lock.
- Messages sent or received will also have an open lock icon.
How do you know if your messages are secure?
To talk to someone via Signal, they must also have the application on their device. You will see it text input field to say "Signal Message" before entering anything. Also, the send button will be blue with a closed lock icon. This indicates that your communication with your interlocutor is private and protected.

Is Signal Messaging From iPhone Safe?
In iPhone, it is not possible to set Signal as the default messaging application. Therefore, you can not use it instead of SMS and therefore it does not have the same issues as Android. All messages sent are secure and private.
The same applies to desktop available.
Source: Fossbytes