I spent an hour recently talking with a semiotics professor who was trying to explain semiotics to me.  He was very patient, and so was I, and at the end of an hour I concluded that semiotics is like Indian chakra-based medicine:  a set of heuristic practices that work well in a lot of situations, justified by complete bullshit.

I learned that semioticians, or at least this semiotician:

• believe that what they are doing is not philosophy, but a superset of mathematics and logic
• use an ontology, vocabulary, and arguments taken from medieval scholastics, including Scotus
• oppose the use of operational definitions
• believe in the reality of something like Platonic essences
• look down on logic, rationality, reductionism, the Enlightenment, and eliminative materialism.  He said that semiotics includes logic as a special, degenerate case, and that semiotics includes extra-logical, extra-computational reasoning.
• seems to believe people have an extra-computational ability to make correct judgements at better-than-random probability that have no logical basis
• claims materialism and reason each explain only a minority of the things they are supposed to explain
• claims to have a complete, exhaustive, final theory of how thinking and reasoning works, and of the categories of reality.

When I've read short, simple introductions to semiotics, they didn't say this.  They didn't say anything I could understand that wasn't trivial.  I still haven't found one meaningful claim made by semioticians, or one use for semiotics.  I don't need to read a 300-page tome to understand that the 'C' on a cold-water faucet signifies cold water.  The only example he gave me of its use is in constructing more-persuasive advertisements.

(Now I want to see an episode of Mad Men where they hire a semotician to sell cigarettes.)

Are there multiple "sciences" all using the name "semiotics"?  Does semiotics make any falsifiable claims?  Does it make any claims whose meanings can be uniquely determined and that were not claimed before semiotics?

His notion of "essence" is not the same as Plato's; tokens rather than types have essences, but they are distinct from their physical instantiation.  So it's a tripartite Platonism.  Semioticians take this division of reality into the physical instantiation, the objective type, and the subjective token, and argue that there are only 10 possible combinations of these things, which therefore provide a complete enumeration of the possible categories of concepts.  There was more to it than that, but I didn't follow all the distinctions. He had several different ways of saying "token, type, unbound variable", and seemed to think they were all different.

Really it all seemed like taking logic back to the middle ages.