You may have possibly noticed that at some restaurants, an increasing amount lately, the owners fail to include a dollar sign in front of the prices of their menus. Maybe the description of the dish is followed by a simple "11" or, even more unusually, "Eleven", or, worst of all, the entirely-lowercase "eleven". What you are looking at is the owner's attempt to psychologically manipulate you into spending more money at their restaurant.
As marketing writer Martin Lindstrom puts it, "The dollar sign is a symbol of cost, not gain." When we see it, apparently some part of our brain is activated and driven to protect our money by figuring out how to get around it. Since in the U.S., negotiating is a woefully overlooked possibility during the myriad transactions we American consumers undertake every day, the easiest way to get around incurring cost is to choose a cheaper item from the menu. By taking away the dollar sign from the menu, the owners are removing the symbol of cost and so all you have to think about is their delicious food and drink.
At least one study, conducted in 2009 by Cornell University's Center for Hospitality Research which is sort of the nexus for these kinds of things, found that removing the dollar sign actually does work. People eating lunch at St. Andrew's restaurant in New York who were presented with a menu that lacked dollar signs spent significantly more than those who received a menu with dollar signs. Spelling out numbers (presumably including all lowercase or otherwise) or removing decimals from numeric values didn't have any impact, the same study found.
There is an entire cottage industry dedicated to designing menus so that they will have the greatest ability to trot customers toward spending more when they dine and probably a lot of it is based on flawed intuitive logic rather than hard science. A long-held concept that the top right corner of the menu is the place where most diners' eyes will settle (and hence where you should put your "stars", menu items that sell well and have a high profit margin, the term for which is a menu psychology industry buzz word) was proven untrue in a simple eye-tracking experiment that eroded years of assumption by finding that most people read menus like books, top to bottom and left to right.
That is not to say that the entire efficacy of menu psychology is based only on removing dollar signs. There are other mind squeezes that actually do work that restaurants use on you all the time. Most notably is the placement on the menu of a high-priced but possibly less-profitable item beside another more profitable item that, on its own, would seem costly but since it's placed for easy comparison near the higher priced item seems like a value. In a dissection of the menu for the restaurant Balthazar, writer William Balthazar called this item the Anchor, as it makes "everything else near it look like a relative bargain". Although not necessarily backed up by a hospitality study, this one is probably accurate.
Perhaps the place where you spend money that is most studied is the grocery store. As marketing people who follow such things tell it, when you enter a grocery store you are walking into an enormous buildings of well-planned series of manipulation, some overlaid upon others, that you encounter virtually every step of the way through your visit. Martin Lindstrom describes a field test where shoppers were confronted with a special on soup for $1.95. Over the course of a couple of days, the group conducting the tests found the most lucrative combination: parquet floors around the display that not only separate it from its competitors but also slightly jostles the cart, causing shoppers to slow as they pass; the price presented without the dollar sign "1.95"; and, most disturbingly of all, adding a maximum amount to the purchase, in this case "Maximum 3 cans per customer", which seems to trigger our sense to hoard valuable things and leads us toward purchasing the maximum amount rather than just the one or zero we would have bought without the sign.
The researchers found this effective combination by changing the dynamics piece by piece in a single store overnight and then watching the shoppers remotely as they fell dumbly under the sway of the power of suggestion. They watch us while we shop a lot, apparently.