And if you're again lucky, you'll have an escort who will have called ahead to check stock to make sure you don't end up in the awkward situation of standing at the info counter to learn that they have none of your books in stock.
(And if you're smart and have the energy, you'll have found out whether the escort planned to give the stores a heads-up about your visit. And if not, you have gotten the list of all the stores and tediously called them, one by one, a week beforehand, to see if they might bump up their stock so you'll have something to sign. Warning: making these calls will more than likely do a number on your ego.)
A Milwaukee bookstore owner looks at what makes for an excellent drive-by (or stop-by) signing, from his point of view. You can read his account of a "dreamy" drive-by signing here.