This type of advertising costs dealers a good amount of money, sometimes adding $300 or $400 to the cost of each vehicle. Some manufacturers such as Honda include this cost within the invoice price so you never see the advertising fee.
However, some manufacturers don't include it, or they have it as an additional line item on the invoice. These advertising fees are usually listed as acronyms such as FDAF (Ford Dealer Advertising Fund) and TDA (Toyota Dealer Advertising Fee).
As a general rule, you will need to pay the advertising fee - most dealers will not negotiate on it. However, be aware that dealers try to pass off other fees by calling them advertising fees when they're really not.
If the advertising fee is not listed on the factory invoice, but the dealer is including it in the final price, this is where you will need to pay close attention.
If it's a legitimate advertising fee, you will see similar fees from all dealers. If one really stands out for being too high, it's a good indication that dealer is trying to pad his profits with BS fees.