Perhaps there was a time when you just stopped doing anything you were supposed to do as a grand stretch limo drove by with their signature tiny flags placed on each side of the engine hood. More often than not, the second thing you would want to determine is the symbol on these tiny custom flags so that you could tell what country the limousine is servicing the VIP inside. When you want to have that special attention from onlookers, you can be sure that you would get them by using some custom flags.
You can ante up the effect of your custom flags by placing them on key locations. Getting to know the right locations would maximize the visibility. For example, placing them on car hood would definitely make them visible, especially as the flags would sway actively against the oncoming wind. Even if the design of cars does not include flags to be placed on them, it is already a welcome sight and makes cars look more important.
If you find this kind of setup quite intimidating, you may try a more traditional approach. For example, placing them on flagpoles by the main entrance of certain places would get that needed attention from visitors. It is plain, simple, effective, and easily recognizable as custom flags are normally seen at this specific location.
You may also do a numbers game. By placing several custom flags with the same theme and message in a repetitive and consecutive pattern, you would be instilling the message again and again, thereby increasing the effect of the suggestion to potential clients. Of course you would have to consider the effect of these flags on the mindset of the people. Too much mixed information may cause confusion. Keep the main theme and message direct and concise, and you may be sure that your custom flags would be serving their cause properly and positively.