Sending S/MIME Signed messages on an Android device

In order to send S/MIME signed messages, an S/MIME signing credential must be added in settings and the Default Encryption Type must be set to S/MIME.

Once the Default Encryption Type is set to S/MIME, choosing the Sign (S/MIME) option during message composition will sign the outgoing message.

Note: See Configuring Message Encryption on an Android Device for instructions on configuring S/MIME preferences.
Note: See How do I create a message on an Android device? for instructions on composing messages and setting message options.