As mentioned earlier, there are many banner types. Each banner specifically displays a message for a particular type of administrative access to the ASA. To set a banner on the ASA using the ASDM, navigate to Configuration | Device Management | Management Access | Command Line (CLI) | Banner. Here you'll be able to set all the different banners the ASA supports:
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Remember, once you're done, click on Apply and save the settings of the ASA.