If you are planning to use Turnitin, you must announce in your syllabus that students' papers may be submitted to Turnitin. Your syllabus should also notify students of penalties and procedures regarding plagiarism.
This is the notice that must be placed in your syllabus:
Clarion University has a license agreement with Turnitin.com, a service that helps prevent plagiarism by comparing student papers with Turnitin's database and Internet sources. Students who take this course agree that all required papers may be submitted to Turnitin.com. While student privacy is protected, papers submitted to Turnitin do become source documents in Turnitin's reference database solely for the purpose of detecting plagiarism of such papers. Use of the Turnitin service is subject to the Terms and Conditions of Use posted on Turnitin's website. Clarion University is committed to preserving academic integrity as defined by the Academic Honesty Policy (http://www.clarion.edu/67758).