There are a few outcomes from advertising, Name recognition for one will not really work out from a ROI point, too hard to measure.
Sales, visits, sign ups however you can track.
You may have a sign on your car that cost you $50 to have made, someone stops you in the parking lot and asks about your service, measurable, but rarely happens. What usually happens is they see your sign, weeks later when looking for service they come across your ad and MANY others, they chose yours, they chose it because they had heard of you before, they may not remember where but they saw your name...
The big problem is if you do not have a big budget, you need to ensure your ROI is at least what you spend so you can repeat... your customers will stay giving you a net profit down the road.