If need to make it clear which items on a project are taxed, first click 'Settings' on the Project.

Then, click Contract Settings and select to show the Line Item Tax Indicator.

Finally, on your projects, your taxed item will be clearly shown.

If you'd like to set this as a default, you (or your account owner) can adjust it from your Account Settings.
You can also choose to show this marker when printing your documents, too.