You can create a 14 day trial account by clicking on Sign In at the upper right corner of OnSign TV homepage. Click on Create an Account and provide your data. You can also login using your Google account by hitting the blue button right below. In this case, your OnSign TV account will be created automatically.
The same action can be done by clicking on Get a Free Trial Account on OnSign TV homepage.
After the 14 day trial you can subscribe to OnSign TV if you are glad with the platform. Check out the pricing plans at this page.