Rocky,
It does seem that these other responses are correct, based on my experience... I also signed up for Courtyard Club at the front desk of a Courtyard by Marriott. The $10 fee was listed on my folio as well as a rebate for all local call charges for that stay. I was assured that the addition of Courtyard Club to my existing Marriott Rewards account would be seamless, and it was.
I did receive a new card, same number just different logo (CY Club Marriott Rewards).
The fact that they send you a $10 certificate toward your next Courtyard stay makes the program free.