Believe it or not, there is actually a legal reason for this. There is a difference between putting up a sign that says fresh fish, and a sign that says "fresh" fish.
The difference is quite simple: Anything that is between quotation marks is something that has been said to someone. Hence, it is the written representation of a spoken assertation. This means that a sign saying FRESH FISH is a claim made by the vendor: That they, indeed, sell fish that is fresh. In that case, it becomes a case of definition: how fresh is fresh fish? If you live on the coast, you can buy fish straight off a fishing boat - that is fresh fish...
The difference, then, is that "fresh" fish doesn't make a claim coming from the vendor, but rather from a non-identified individual, and as such, it is a freedom of speech issue (anyone is allowed to say that a fish is fresh, no matter how old it is, and no matter how valid the claim of freshness), versus a legal issue: A vendor is not allowed to make false claims about his produce. If he sells fish that is 8 hours old, some people would claim it is not fresh, and hence the claim is false.
All semantics, but quite clever. Now the only question that remains is if the vendors actually know all this, and put quote marks around their claims because they are clever, or if they don't know, and just put them there out of sheer ignorance, because they feel it looks clever (see greengrocers' apostrophe)...
As for "Casual Attire" - this one is a bit more tricky, although logically, it would be the written representation of what the bouncer will tell you, if you ask him what the dress code is. Or perhaps the manager, if you were to ring the restaurant in advance, to ask about dress code. If the sign said Casual Attire, perhaps some dimwit would walk in and ask where the section for children's clothes is. I dunno. | 
