Illegal stamps are postage stamp-like labels issued in the names of existing independent countries or territories used to defraud postal administrations, stamp collectors, and the general public.
Often, but not always, a member nation of the Universal Postal Union (UPU) will have asked the UPU to issue an "International Bureau Circular" advising others of the illegal stamps.
There is no definitive method to identifying illegal stamp issues.
Illegal stamps are said to result in adverse consequences for several different parties.
In addition, inexperienced or non-philatelists have been tricked into buying illegal stamps that are worthless memorabilia for their favorite hobby or interests.