It seems strange that anyone would take offense at a garage sale, doesn't it? But many local governments, town ordinances, and neighborhood policies forbid or restrict yard sales for a variety of reasons. If you're planning on holding a sale in the near future, it would behoove you to take a look at your local ordinances to make sure you aren't violating any regulatory restrictions.
Since the rules regarding garage sales vary so widely from state to state, county to county, and even town to town, it's impossible to make an all-encompassing list of what you'll need to do for your garage sale. Some examples might be helpful, however.
In Dallas, Texas, you may have two sales per year per property; signs may only be placed on the property where the sale will take or is taking place; and the sale cannot last for more than three consecutive days. In Frankfort, Illinois, you must have a permit, which costs $5; all signs must be free-standing; and you may have up to three sales per year, but they must be 90 days apart.
Your area might have similar regulations, so check online or send the local town hall an e-mail or phone call. Generally, restrictions will be found at the local level, although some will be at the micro-level (your Home Owner's Association or apartment policies, for instance) and some are the government level.
The Consumer Product Safety Commission released a report in 2009 stating that garage sales found selling toys that are considered potentially hazardous for children or others can be prosecuted. You probably don't need to worry about the CPSC visiting your yard, but it does bring up an important idea -- are you marketing any dangerous items? This includes any toys that have been recalled.
If you find out that a permit (and/or permit fee) is required, consider whether the price of the fee is worth it. Hopefully you'll make that much money back, but if you aren't sure, maybe you should see if you can donate your items or give them to a friend to sell.
And if you find out that there are no regulations stopping you from holding your garage sale, start planning! Don't forget to stop by GarageSaleCow.com to freely advertise your sale and find other treasure troves in your area.