Placard, Marking and Decal
 

Hi guys,
What is the different between placard marking and decalIs there any reference documents that list out their main different ?

There are several variations to this, but the most common is "placards" and "markings" are regulatory terms that provide pertinent information, and decals are simply decorative in nature. For example, in the FARs only the 2 former terms are used where placards provide certification information and markings provide identification information. However, you can get into semantics when various terms are translated from one language to another.

What aircraft would help if any?

ATA chapter 11 in the AMM would be aircraft specific.

I thought decals were slide transfers. Placards tend to be secured by some form of adhesive or screwed on. All the same thing really, crew information.