The rate of obsolescence of a sign seems to be nearer to that of an automobile than that of a building. The reason is not physical degenera¬tion but what competitors are doing around you. The leasing system operated by the sign companies and the possibility of total tax write-off may have something to do with it. The most unique, most monumental parts of the Strip, the signs and casino facades, are also the most changeable; it is the neutral, systems-motel structures behind that sur¬vive a succession of facelifts and a series of themes up front. The Alad¬din Hotel and Casino is Moorish in front and Tudor behind (Fig. 13).