Signet could and should give the following bonuses in order to keep people interested in conquest and actually try to make their country first:
Exping in an area controlled by your nation: +10% Exp
Exping while your nation is first: +10% Exp
Exping while your nation is second: +5% Exp
Exping while your nation is last: +0% Exp
This brings the total maximum exp bonus to +20% - 5% more than ToAU's maximum exp.
Here's the kicker:
Your party consists of 2 Bastokans, 2 San d'Orians, and 2 Windurstians. Where do you exp?
It would, however, disperse exp parties out of overcrowded areas, such as Boyahda, Valkurm, Qufim, etc. If Valkurm was under San d'Orian control, and you're Bastokan, would you not to go Bastokan-controlled Buburimu to exp instead?
The idea has quirks that could be worked out, but the idea is there. Being in first place should give some kind of cool bonus with Signet. (Obviously this wouldn't extend to ToAU areas or Lumoria)