On Apr 5, 9:15*pm, Eric Greenwell wrote:
If knowing the call sign is important, there should be a requirement for a
number on top. Failing that, I suspect it's just habit and inertia that leaves
the lower wing contest number in the rules.

The primary original reason for contest numbers was visual ID on
starts and finishes. The only contest-relevant reason for them today
is assessing penalties on infractions within line of sight of the CD
(e.g. finish penalties).

IDs are helpful in making traffic calls irrespective of their initial
logic for being. Most of the time these calls are for gliders turning
inside you (belly to you) or abeam of you. An ID on top of the wing
might help on occasion, but in most instances where it would be of
help the higher glider either doesn't have a clear line of sight
(can't look through your own fuselage), or is in a better position to
clear the conflict on its own.

9B