If you open the Explorer's Pack, you get a set of treasure maps. One set for each alliance.
These sets take up space so obviously you want to put them in your bank.
However, you can't store the sets in the bank, you have to open them. Once you've opened them you can put the individual maps in the bank but that uses up most of your bank slots.
So you have a choice, walk around with a few character slots permanently filled or fill up half your bank. Unless, like me you didn't know this would happen until it was too late.
Now I have next to no bank space left.
'Clever' sigs get old real fast - just like this one.