Gaffers tape, or black shoe polish in the dispenser bottle with the sponge
applicator.

"Matt" wrote in message
...
§ 45.29 Size of marks.

(h) After March 7, 1988, each operator of an aircraft penetrating an ADIZ
or
DEWIZ shall display on that aircraft temporary or permanent nationality
and
registration marks at least 12 inches high.

Interestingly, my 1979 152's N-number is 3 inches high. Now where did I
put
those "temporary registration marks"?