How do you make a Deals System that randomizes decals?

Hello I'm new to Unity, I am trying to figure out how to make a system that can randomize decals so I only have to use one shield (mesh) with many decals, instead of many shields with different diffuse textures. For I want the decals to work for certain factions. Like for the one nation, it will have a random set of patterns based on their faction. Then for another faction, the same shield will have their patterns instead of the first faction's.

A example of this is like in Rome II Total War, where each factions uses different decals for the same shields:

Carthage:
http://img4.wikia.nocookie.net/__cb20130802204123/totalwar/images/7/79/Rome_ii_total_war_11.jpg

Athens:
http://i43.tinypic.com/2d858ht.jpg

Dose anyone know of a tutorial or anything showing how to do this? Thank you for reading this question I hope to hear from you.

 

You could try to use Standard Shader's detail Albedo texture, and maybe Detail Mask texture if needed. Then you can randomly shift the detail Albedo offset