A sign post for mission creators to display custom text or global values in missions as players taxi around would be really helpful for some custom missions.
For example; Imagine having a game mode where you bring troops to a hanger to add lives and unlock a new jet. Each hanger is labeled with the jet it unlocks, all you have to do is bring the troops inside.
It could even be used to display a scoreboard via global values near your respawn point so you can see the score at a glance before you take off.
There could be many more uses, but I think a customizable sign would be an awesome addition to provide extra information to the players when making missions.