In details, is all about the commercialization of public space for private gain? Should outdoor advertising be banned?
Are you talking about billboards, or more widely to the light signage that goes on the sidewalk beside premises as well?
Both, IMO, should be much more strictly regulated, they are unsightly, and usually contain too much information for a casual drive-by to get any use from anyway. The lit ones not only use energy that, in this current climate, we should be conserving, but also cause light pollution and distract wildlife such as migrating birds. The plastic handmade signs that you see along the roadside are even worse, they really are litter, and highly unfriendly to the environment, those ones should absolutely be banned and offenders fined.
Along busy roads there are usually so many billboards that I highly doubt they are effective anyway, as you kind of visually tune them out. In the city they amount to little more than expensive litter, and in the countryside it's tantamount to vandalism! Many of them too walk a fine line for me as a parent, having to answer questions from my kid that I don't think are appropriate for her age – and I really am no prude.
* Viridian steps off her soapbox, and clears her throat* Sorry about that, you kind of hit a nerve there!