I noticed that many food service trucks on the road have a sign or signs on them that read “FISH.” I was wondering if transporting fish products is any more of a health or safety concern as transporting pork, beef, or chicken. I often see the sign on the sides of big grocery chain 18 wheelers which obviously are not full of just fish. I believe that there is even a “FISH” sign on the side of the Schwan’s delivery truck where the fish is packaged and frozen! Who needs to know that the truck happens to be carrying fish? Is there a hazzard we drivers should know about?!
I have noticed this as well and have wondered about the reasoning.
I did a quick search and perhaps have found the answer although I’m not sure.
http://policy.fws.gov/241fw2.html
I’m thinking that these trucks sometimes carry live fish (e.g. lobsters - although not technically a fish) and an oxygen supply is necessary to keep them alive. So perhaps the FISH sign is a warning that oxygen cyclinders may be on board and are a fire hazard in case of an accident.
This may be totally wrong since it seems it would make more sense to have an “oxygen” sign on the truck instead.
I hope that somebody knows the answer to your question since it has baffled me as well.
Don’t vehicles carrying compressed oxygen tanks have to have a “FLAMMABLE” (sic) diamond sign on them, anyways? I’m pretty sure that they do, which makes the extra signs rather pointless.
Perhaps it’s a public service to seagulls or bears that might otherwise not know which trucks have the fish in them.
They do not want the contents being transported to be mistaken for liver.
Because rotting fish smells worse. 
Seriously, it may be there to remind the people in charge of logistics that the cargo spoils faster and so they should give it priority for loading, unloading, and whatnot.
The oxygen thing is definately a red herring. I have transported many live fish destined for stocking purposes and not destined for the market, and we never had the “fish” sign on it. I’m not certain, but I suspect that it has to do with regulatory purposes related to the harvest of fish. That is, a conservation officer (game warden) would know that these people have the permit to carry large amounts of fish that may not be readily identifiable. Sport fishermen transporting fish in some cases are required to keep the heads and fins on so that conservation officers can identify the fish easily and tell how long it was (for length limit purposes). Obviously, those rules would make it hard for commerce in seafood, so there must be permits that get around those limits.
Fishhead
My guess is that Fishhead is on the right track.
At first I doubted that there was a law about this, but the Ohio Revised Code has a section detailing the requirements which include
So, it’s a law. Looking for the exact reasons.
I thought they FISH signs were for Christians who love to read…
Thanks for the clues. I found this website which shows how involved the state’s fish and game agencies are involved in all forms of the fish business, even if the fish is frozen. processed, from another state, are destined for private homes, resturants or whatever (this website is from Louisiana, but I found a few others). Apparently there are tons of regulations designed to protect the nation’s wildlife resources so that commercial fisherman don’t go buck wild and overfish a certain species, try to sell a species that is illegal, try to harvest immature fish, or use illegal means to harvest the fish. I am guessing that by displaying the “fish” sign, even though they are carrying other forms of food, the owners of the truck are saying “Yeah, I am carrying fish, I got all the liscenses, I don’t have any species that I am not supposed to have, it was caught by legitimate liscenced fishermen by legal means, it is all properly packaged and marked by a liscensed processor, you are welcome to see my cargo and my records.” So it is not the health department or the highway department that cares that a truck is carrying fish, it is the Fish and Game guys. I guess that there is no agency that cares what kind of pig, chicken, or cow you have slaughtered, so therefore they don’t have to have a sign that says “Beef” or whatever on the side.
http://www.wlf.state.la.us/apps/netgear/index.asp?cn=lawlf&pid=586
Another possibility is that many people are deathly allergic to seafood. In some cases, the allergy is so bad that even touching water or metal that has come in contact with shellfish weeks before will lead to anaphylactic shock. The sign could serve as a warning to emergency personnel with allergies that they should be careful of what they touch. I couldn’t find any information on the web to support or disprove this theory though.
Of course, by that standard, there should be trucks riding around with giant “PEANUTS” signs on them.