http://www.unsolicitedmarketingadvice.com/2006/11/07/billboard-basics-six-rules-of-thumb-for-creating-outdoor-advertising/
Some of these apply to this situation.
Misconceptions abound with billboards, but there are a few basics that can help structure your outdoor advertising strategies:
1. Secondary, not primary
In general, billboards are a secondary medium, not a primary one. This means that they act as a support to other parts of an advertising campaign, and are not the main thrust themselves. There are exceptions, of course. Retail operations like gas stations, hospitality, restaurants and such will use outdoor advertising as a primary vehicle to get people to “exit now.” But if you’re selling an intangible product or service, or if your goal is to develop your brand image, then you need to have a plan that goes beyond billboards.
2. Six Seconds, 6 Words
Billboards are viewed quickly, generally in vehicles going over the speed limit. This means there isn’t much time to read a complex message. The industry rule of thumb is that a billboard is read in less than six seconds, and the billboard should have no more than six words. You can have a few extra words in smaller type or a secondary position to give location information or a call to action, but your primary message should be 6 words or less. Generally, it should stand away from secondary text and presented in an uncluttered manner. Once again, less is better, just as Mark Twain once said, “If I had more time, I would have written less.”
3. Avoid Metaphors
The need for simplicity is an obvious corollary to the speed and brief message space of a billboard. In Web design, Steve Krug has said “Don’t make me think.” The same concept applies to outdoor advertising. Comparisons should be clear, and while they may be clever, they should be immediately obvious. If you see a concept like this one for IBM and say, “I don’t’ get it,” then you can be confident that the metaphor just isn’t working (Original post: Adrants)
4. Mnemonics Only
When I’m driving with someone, I don’t want them taking their hands off the wheel to write down a phone number. Unless one has some great phone number that spells a simple phrase, don’t even think about using one. Likewise, caution should be given to using URLs, and they must be simple, straightforward and memorable.
5. Buy in Gross
Generally, you’ll want a billboard campaign. So be ready to spend some money. A single billboard will not achieve your communication goals unless you can use the best, most well known billboard phrase: “Exit Now.”
Billboards are bought in “shows,” which are comparable to gross rating points. If you buy a 50 show in a particular geographic area, you will be reaching a number of viewers equivalent to 100% of the population in the area every two days. This is based on the amount of traffic known to go past the board (the Annual Average Daily Traffic, or AADT), the number of people age 18+in each vehicle, and the hours of illumination for the display. Of course, this doesn’t necessarily mean you’re reaching the population that actually lives in the area – especially if you’re posting on expressways or commuter routes.
6. Placement Review
Not every billboard is a winner. In fact, the smaller your organization or your budget, the more you’ll need to do hand-to-hand combat in selecting billboard locations. In addition to different sizes, placements on the opposite side of the road (called cross reads), tall buildings and trees can significantly impact each of your placements. Nowadays, most companies provide a photo, map and description of each placement; although the photos do not always do justice to individual boards, making an automotive survey something worth considering.
Apply these six basics and you’ll be well on your way to successful outdoor advertising effort. Explain them convincingly to your clients, and you’ll be well on your way to a successful campaign — and marketing career.
