You abide by the state law you are presently in. If the state law is must notify then notify. If the there is no state law to notify, then it's up to you.
I do not notify. It invites actions that make the environment unsafe (stranger trying to empty a firearm they are unfamiliar with is extremely dangerous.) The safest place my firearm can be is in its holster not being handled. If a traffic stop has nothing to do with your firearms then why complicate the situation by bringing firearms in? If it did the officer would approach appropriately and make his intentions clear, well before you would have the chance to notify.
I also don't notify my garbage man, or the hotel desk person, or anyone that doesn't need to know "out of courteousy". As treo puts it, voluntarily notifying is like submissive urination by a scared puppy, hoping the officer doesn't beat you.
My advice though, is follow the driving laws as strictly as you follow federal firearm laws, and make sure your vehicle is running 100% so you don't get pulled over. Beyond that, don't do anything more than the law requires.
“One of the illusions of life is that the present hour is not the critical, decisive one.” – Ralph Waldo Emerson