Copyright protection arises automatically whenever a "work" is fixed in a tangible medium of expression. I see no reason why a bumper sticker cannot qualify for copyright protection. But if you want to enforce your rights against infringers, you will need to register each bumper sticker with the U.S. Copyright Office. Registration is one of the great bargains of all time---at a cost of $35 per work you buy substantial protection. Moreover, if you register within three months of first publication, you are entitled to statutory damages and attorneys fees. One interesting issue is when and how one publishers a bumper sticker---I supposed the first date of publication would be the date someone attaches the sticker to a bumper (although it might come before if copies of the bumper sticker were published in print earlier),
Bumper stickers are either automatically entitled by Federal law [17 USC 102] to copyright protection or to trademark protection if used in commerce, depending on the nature of the bumper sticker, otherwise they are public domain. You need to see an Intellectual Property Law attorney with the specific to find out if a specific bumper is protected by intellectual property rights.
As to copyright, that is exclusively FEDERAL law, so it is protected the same throughout the US, with rare exceptions. So, that lawyer can be anywhere, even outside NY.
I am not your lawyer and you are not my client. Free advice here is without recourse and any reliance thereupon is at your sole risk. This is done without compensation as a free public service. I am licensed in IL, MO, TX and I am a Reg. Pat. Atty. so advice in any other jurisdiction is strictly general advice and should be confirmed with an attorney licensed in that jurisdiction.
Very few phrases that can fit on a bumper sticker are copyrightable because they're simply too short. But if you create and display one or more graphic designs on the bumper sticker -- with or without a word or phrase also present -- then perhaps the design(s) is copyrightable. If so, speak with your own copyright attorney about registering the copyright in that design(s) with the Copyright Office. You should hire a NY-licensed copyright attorney because your goal is to exclude all others from selling the same or similar bumper stickers and your state's particular law of unfair competition will apply.
The above response is general information ONLY and is not legal advice, does not form an attorney-client relationship, and should NOT be relied upon to take or refrain from taking any action. I am not your attorney. You should seek the advice of competent counsel before taking any action related to your inquiry.
Assuming that the work has sufficient creative expression so that copyright interest applies, your copyright protection affixes automatically. That is, you do not have to take further action to claim a copyright ownership. But registering the work with the US Copyright Office is required before you can enforce any infringement action in federal court and doing so early and before a problem arises has many benefits including the right to ask the court to apply statutory damages because in many cases "real" damages are very hard if not impossible to prove out.
I suggest that you consult with a lawyer in private and discuss your objectives in more detail. If you plan on starting a business I'm sure you have a lot of other questions as well. You can start by calling around to several for a free phone consultation, get some insights then pick the best fit to work with. I will link you to a brief copyright law overview that covers the basics below.
DISCLAIMER: this is not intended to be specific legal advice and should not be relied upon as such. No attorney-client relationship is formed with the law firm of Natoli-Lapin, LLC on the basis of this posting.