In the city of 300,000 where I live, there is a limit on how many garage sales you can have in a year. They are limited to three days each, and have to have at least six months between sales. We have one sale in late March or the first weekend in April, then another in late September or the first weekend in October. Thursday is a GREAT day for sales here. We run ours Thursday-Saturday.
We have a neighbor who would turn us in without hesitation if we tried to have the sales less than six months apart. I have some professionally made signs that I reuse. I do not put the date on the signs, just GARAGE SALE, the address, and TODAY 8am-3pm. I ordered these from vistaprint.com and they work great! Weatherproof and very sturdy. We advertise on craigslist and spring for an ad in the local paper. I have tried skipping the newspaper ad to save the $33, but I really notice an increase in traffic when we place an ad.