If the goal is to get the attention of avatars whether it be signs, products, or some other attraction then such items should be rezzed at eye level. In the real world many retail stores will place merchandise at just before or at eye level, however in virtual worlds the most common eye levels are actually the avatar’s should up about two meters above the avatar’s head (sometimes referred to as camera angle and position). This is why, unlike in real life stores, many in-world stores stack items from the floor all the way to the ceiling.
However, as with any marketing methods there are always exceptions to the rule. When an avatar is in a seated position their camera position will be closer to the floor. This is also true for some of the smaller avatars in virtual worlds which is similar to real life stores who will place items such as toys and cartoon cereal boxes closer to the ground so that those products are at eye level with kids. Depending on the circumstances, an avatar in a seated position might also be in mouse-look view in which case the camera position and angle is from the front of the avatars eyes just like in real life. Shoppers tend to scan merchandise in the same method as they read a book (i.e. left-to-right such as in the western hemisphere) and will usually find the most expensive items at eye level which the lesser expensive or generic brands are located on the very top shelf or close to the floor.
The visual impact of wall decorations such as art, paintings, and photographs should also be located at eye level even if the room has a high ceiling. When rezzing such items keep in mind that the size of the artwork should be proportional to the space. Small pictures should not be placed on large empty walls and huge paintings should not be located on small walls. When there are several small decorations to be rezzed in an area they need to be clustered together with a common theme in order to fill up the space.