(a) Except as provided in paragraph (f) of this section, each operator of an aircraft must display marks on the aircraft meeting the size requirements of this section.

(b) Height. Except as provided in paragraph (h) of this part, the nationality and registration marks must be of equal height and on—

(1) Fixed-wing aircraft, must be at least 12 inches high, except that:

(i) An aircraft displaying marks at least 2 inches high before November 1, 1981 and an aircraft manufactured after November 2, 1981, but before January 1, 1983, may display those marks until the aircraft is repainted or the marks are repainted, restored, or changed;

(ii) Marks at least 3 inches high may be displayed on a glider;

(iii) Marks at least 3 inches high may be displayed on an aircraft for which the FAA has issued an experimental certificate under §21.191 (d), §21.191 (g), or §21.191 (i) of this chapter to operate as an exhibition aircraft, an amateur-built aircraft, or a light-sport aircraft when the maximum cruising speed of the aircraft does not exceed 180 knots CAS; and

...........

This is why I claim my max cruising speed is 179.99 KCAS.  Be careful of the green arc markings on your AI as a Fed might interpret the top end to be max cruising speed (Vc).  Refer to this for the definition of "cruise".  To wit:

http://en.wikipedia.org/wiki/Cruise_(flight)

Opening line:  Cruise is the level portion of aircraft travel where flight is most fuel efficient.

Or V speeds for Vc:

http://en.wikipedia.org/wiki/V_speeds

One might argue that "efficient" cruise is when operating LOP and that knocks a few Knots off the airspeed.

Grayhawk

My understanding was numbers should be one foot high if plane exceeds 200 knots, but I have seen many 360s with 3 inch numbers, and am sure these are 200 knot planes.  I plan on a little over 200 knots, what should I do?

Ed Gray, Dallas L2 building