You can add an estimate leave signature message, this is what the customer will read when the engineer leaves and if they agree they will sign. This can include any necessary information or disclaimers or a simple acknowledgement of the engineer having attended the site.
In the list of mobile settings click 'Estimate leave signature message'.
You will see a page with 2 choices. Click 'Yes' in order to set up this message. Then you will see a box where you can enter your message. When you are happy with this message click 'Save'.