Every time you go out to dinner, out on the table is some sort of table display. Some are less expensive such as the 4-sided Table Tent. Others are in plastic on the table, or are some similar setup. They all work in the same manner upon the table. Most look like something similar below.

This particular item is really a very simple use of marketing. When people sit down they are interested in specials, and drinks, and having an item like this on the table is an easy item for the customer to pick up and look at.
Most restaurants use items such as above to show off their dining specials, specialties of the house or their wine menu. It is also useful to show off special events and upcoming menu items. Items such as lists, and short paragraphs explaining a photo is all you need. Nothing further in the display and the customer will be interested in reading. The information needs to be brief. Also what needs to be remembered is the customer will more than likely be reading under poor light and not reading light. They are also dining to be with the people they came with. Anything more is just too much.
A restaurant such as Olive Garden, or Ruby Tuesday's might feature an upcoming item coming on their menu with a photo in order to get their customers interested in it, and to come back, or an item just added to the menu.
Any restaurant who wants to get information out to their customers, this is the way to go. Using an item such as this, can help to bring in more profit.