^
Oldzimm - A lot of those citizens weren't quite so law abiding.
From what I remember a big reason for that on Katrina was because of the high criminal element in N.O. that was going door to door looting and taking peoples guns, etc. out of their homes after the people that evacuated had already left.
Also martial law doesn't automatically mean they will come en-mass and do house to house searches to collect firearms, normally martial law means there is a curfew and that if you are caught breaking the law (killing, rapeing, rioting, burning buildings, stealing, etc) you will likely be dealt with a lot more severely than normal including possibly death by firing squad.
If you have any weapons over about 3 to 5 yrs old its likely they have no record of its purchase now even if you bought it at a store and it was registered, most states and the Feds don't keep the sale of firearms on record longer than 3-5 year period of time.
If things ever did get so bad that the govt ever did notify that they would be coming around to do searches and collect firearms a person could always get some 5" diameter PVC sewage pipe and end caps and PVC glue to put the weapons in and then seal them in to make them moisture tight and then bury them out in the yard or woods nearby. Lube them up real good with gun grease (cosmoline) if you think that you'll leave them buried for more than a few days.
Not saying thats the type of thing that i'd do but a person could do it.

(wink wink)
Does that make me an outlaw? Perhaps yes but if things in our country get that low that they are going around en mass to collect everyones guns no matter where you live then you have to do what you feel is right to protect yourself and your family because one thing is 100% sure and that is that all the criminals will keep their guns and it would only make them too happy for all the law abiding citizens to turn theirs in.