Such activity as advertising will certainly gain the notice of the locals and begin a chain of rumours. So will almost any other unusual activity. Even the departure of a party from a town is likely to be noticed. Obtaining such news is usually merely a matter of making the rounds of the local taverns and inns, buying a round of drinks (1d6*10 Gold Pieces), slipping the barman a few coins (1d10 Gold Pieces) and learning what is going on.