When I write my config like this:
323: 16
It doesn't let me stack signs, but if I write it like this
SIGN: 16
It does

I like to use item IDs rather than the words associated with them, as sometimes they can get difficult and you aren't exactly sure what the true word form is.

Sorry about that. I was away and forgot to implement it when I got back. Works great thanks. Hope you can get shift-click to work.

Version 0.8.3 so this should be officially fixed.

The test version should have this fixed. It can be found here: https://github.com/haveric/StackableItems/tree/master/versions/test

I'll try to get an official update out tonight that includes this.

Please let me know if the test version fixed the issues you were having or not. I'm going to delay the official release until I hear back from you and because I am in the middle of getting shift clicking working which I want to get in this update.