This is what happens when you have too many AV marks

Since you cannot hold for than 100 Alterac Valley Mark of Honor, any extra Marks
will be mailed to you.
You must spent some Marks of Honor, only then you can move the Marks of Honor from
mail to inventory.
Completing Concerted Efforts quest requires 1 Mark of Honor from each PVP battleground, it rewards 314 honor points and 12 gold.