on browen weber's site, who is probably in the upper echelon of high profile bakers, she says she'll make 'inspired by' characters, which i take to mean she changes just enough of it to avoid any hassle. while i don't have a bakery (yet), we do have a trophy shop and do some shirts on the side, and every now and then we have this issue. my personal opinion of it is as long as you do only a piece or two, then it's advertising (not to mention if you don't do it, then the copyright owner still gets nothing). i understand their position, but it's a lose/lose/lose for everyone... unless you purchase the license or use licensed material (which is usually pretty generic). don't get me wrong, i still don't use licensed material, just saying my opinion is restrictions could be loosened up to benefit everyone.
while not specific to the decorative end of baking, there is just enough legal precedent to make certain copyright matters a gray area. for example, using characters in satire is absolutely protected. several years ago a judge ruled in favour of an artist for using barbies in uncompromising settings. sure, mattel wasn't happy. my understanding is that in general a copyright can be an expensive pain to enforce if there's an honest question about the purpose of 'infringing.' if you get caught using a copyright, you'd first receive a 'cease and desist' order and that's typically the end of it. having an LLC is just smart business to being with, but it protects your business from absolute ruin in a lot of cases by limiting the damages ('limited liability company'). and, honestly, disney doesn't want to take you to court, they just want to protect themselves. in the real world, no small fry gets hit with these ridiculous fines that *i've* ever heard of, unless they refuse to disobey a cease and desist of obvious infringement. that's not to say you wouldn't be the person they decide to make an example out of.
in the end, there's what the copyright office tells you and there is some legal precedent on certain issues that makes some things murky at best. what's likely is by the time you're served with a cease and desist you've made hundreds of the items in question, so you stop. the copyright cops aren't going to break your door down in the middle of the night. if you persist, you can really screw yourself up. they will take you down, but you force them to do so by that point.
the best bet is not to do it, but if you do then find out how much has to be changed to protect yourself. but, by the time you sit down to design a relatively legal rip-off, you've got more time in it than anything else and your profit margin is shot, your product is suspect, and now you're tripping into some moral areas as far as some customers are concerned. best idea is just to say you can't do it for legal reasons and let them come up with a Plan B. ...or buy the license which can be several thousands of dollars depending on what it is. (i'm in ohio, and as memory serves, buying the rights to use Ohio State University logos was about $800 many years ago. someone feel free to correct me if i'm wrong, as i might not remember the exact amount and i passed on getting one.)