Compound term: special permit.
Erityislupa appears in our example in the adessive singular, erityisluvalla.
Erityislupa is a compound term which comes from erityis- (from erityinen, an adjective meaning ”special” or ”specific”) used here as a modifier plus lupa, a noun which means ”permission” or a ”license.”
One meaning the adessive case takes on is when you want to say something is done ”by” or ”with” something. That is the meaning here: ”with special permit” or ”by special permit.”
Let’s translate the rest of the parking sign, ”Vain torikauppiaille erityisluvalla,” or ”Only for market traders with special permit.” (Note that like many newspaper headlines, part of the meaning is implied.)
Vain means ”only” or ”exclusively.”
Torikauppiaille is another compound noun, this one coming from tori (”market” or ”market square”) plus kauppias (”trader”). It appears in the allative plural which here means ”for the market traders.” (Allative has the basic meaning of ”onto,” but this is a use of the allative similar to pöytä kahdelle or ”a table for two.”)