I assume you mean rooms you have reserved for out-of-town guests.

Very simply:

A block of rooms have been reserved at a special rate for our out-of-town guests at (hotel name). Simply mention (wedding party name) to obtain this special rate.

This will let your guests know where to stay and that they are responsible for paying for the room.
If you are paying for the rooms, advise your guests to call you to confirm the reservations so that you are not paying for an unoccupied room!

Hope this helps & congratulations on your impending nuptuals!