Not sure if you should sign up for the SAT, or ACT for that matter?

Here's what Siena's Director of Admissions Katie Szalda says: 

Siena has been test-optional for years, because we know that a single score can't define your potential. But if you think you could do really well on either test— or if you're applying to colleges that require those scores—go ahead and take it. If you're happy with your score, we're happy to take a look.

Bottom line is: Not sending in your SAT score won't hurt your chances at Siena, but sending in a good score can help enhance your application.