Numerous standards suggest or require the use of a login banner that clearly informs legitimate users and attackers that the system is for authorized users only. Substitute in your organization's banner below if this standard text isn't sufficient.
cat > /etc/banner <<EOF
Authorized Users Only!
Any attempted or unauthorized access, use,
or modification is prohibited. Unauthorized
users may face criminal or civil penalties.
The use of this system may be monitored and
recorded. If monitoring reveals unauthorized
use than records may be provided to law
enforcement.
EOF
uci set 'dropbear.@dropbear[0].BannerFile=/etc/banner'
And don't forget to commit your settings!
uci commit
Here's the script in github for easy download: https://github.com/SpotlightCybersecurity/openwrt-scripts/blob/master/banner_setup.sh