All forms of advertising have something referred to as a CPM or 'Cost Per Thousand' ['M' being the roman numeral for thousand].
This is simply the cost per one thousand exposures to your ad.
It's used in advertising as one way to measure the reach of an ad because it shows how much it costs for an ad to be seen by 1,000 people. For example, you calculate the CPM for a front-page ad on a national newspaper the same way you would an ad in the middle of the neighborhood weekly paper or a Super Bowl ad.
To understand the way we calculate this we use simple math:
Divide the total number of impressions the ad will make by 1,000. For example, if your ad would make 10,000 impressions, you would divide 10,000 by 1,000 to get 10. Divide the total cost of running the ad by this number [10 in this case] to calculate the CPM for the ad.
One factor to keep in mind is longevity or time.
Because signs last for so long and the are typically placed with much careful consideration this drives the CPM down to lows that no other form of advertising can touch.
So when you calculate the cost of exposure of your signage you really have to keep in mind that its longevity is going to keep the total exposure up leading to lower prices per thousand views!