The only way to guarantee something will be done is to arrange it yourself (and pay for it if necessary - like ordering a custom cake or a basket or flowers, or arranging for one of the celebration packages). They can usually print up some menus with Happy Anniversary written on them and maybe the celebrant's names. They can usually do that right at the restaurant. Sometimes more is done, sometimes it isn't. Sometimes a free dessert or other item will be given, sometimes it won't.