When you book a client manually, you have the option to choose "No Contract". When this is selected neither you or your client will be required to sign an online contract.
To begin, navigate to the shoot and click the Book option in the shoot's sidebar.
You will be prompted to Choose from Book Online or Book Manually.
When you choose the Book Manually option, you will go through the process of creating a booked job, but you can choose to have no contract for the booking under the proposal's Contract setting. This option is not available when you Book Online.
One important thing to note is at the end of creating this manual booking, you will simply have created a booking. Nothing is emailed to the client, so if you want to notify them of the booking, you can send them an email (and use one of your email templates) or you can email them send them an invoice notice if they need to pay you.