Bloom, Plume, Mold.... All the same thing:
"Mold (or mould) is a term used to refer to fungi that grow in the form of multicellular thread-like structures called hyphae. Fungi that exist as single cells are called yeasts. Some molds and yeasts cause disease or food spoilage, others play an important role in biodegradation or in the production of various foods, beverages, antibiotics and enzymes"
There is bad mold, that green stuff we see on old bread, and there is good mold, penicillin. The process of fermentation is on the edge of mold - it is the result of the same process but of the single cell yeast - this results in the sugers and the crystalline structure that we see on our tobacco.
I have been a cigar smoker for 20 years and have, like jon11 said, looked for bloom on cigars. it does make a difference in the sweetness of the tobacco because of the sugers produced in the fermentation process.
When you see bad mold on tobacco - that is usually the result of some sort of biological contaminant being present. If your tobacco or cigars have been stored properly (especially sealed tins) then it is probably good mold or what we like to call bloom or plume - this does not mean that bad mold can't happen as contaminants can come from the factory.
Best test is like what many of you have said - smell
