It seems that currently there is no possibility to add agent signatures to outgoing messages automatically (neither in v2 or v3). The email footer can have signature details, but they are added in the very bottom of the whole message, after all other discussion.
I would prefer a checkbox (default checked) "Add a signature" in the reply screen. The signature template could be common for all the agents (easy to change some content like business hours) with a placeholder for the agent's name. In the agent's profile, there could be an option to override the whole signature.
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