At a minimum, a status marker showing “flying” or “climbing”. The closest icon for that now might be the bird cage icon.
Better would be a wing icon with two digits to represent range in inches, and let players convert inches to their scale if they want. (In GURPS 1" = 1m, in D&D 1" = 5’, in Savage Worlds, 1" = 3’, etc.)
Even Better: The two digits would be drawn from a character field, like the HP field, or an Attribute.
Even More Better: The character token is about 10% smaller when flying, offset, and has a shadow showing it’s actual location. A vertical bar overlapping the icon scales to indicate height in inches.