Lockette is a plug-in where you have the ability to indicate whether it's locked or not. I almost forgot about this to be honest with everyone. It is what I used on an old server which was shut down. Basically you're able to format it like this.

1. Place a sign on the desired chest you want to lock.

2. On the sign indicate the following:

-Player who has access

-Several other things, as mentioned I almost forgot about this so I've forgotten how to set it up exactly.

This, without a shadow of a doubt, would help Factions keep their members from taking from other's chests.