Hi CommandoBob, I understand the desire for such a symbol connected to the veteran plane function of an airport, very well and it would do a lot of sense. Unfortunately this can´t be done without changing the Civ 3 code.
Different from the fortress symbol for cities in era 3 and 4 in CCM, the veteran airplane flag in the editor has no own graphic in Civ 3. As you posted, Firaxis connected the Civ 3 airport, that is a combination of airtrade and veteran plane flags, and the graphic for it sadly to the wrong flag (airtrade). The fortress symbol for cities, that is connected to the city wall improvement, could be done easily by changing an existing graphic for walled cities that is connected to the "walled" flag in the editor. This is not possible for the veteran airplane flag with the existing Civ 3.exe.
May be a genius like skyer, skyer2 or the friends of Knuckles could do this by hexediting the Civ 3 exe, but not me.