I have done some research on this and if any folks out there approach a CPA here are some talking points to discuss:
According to the 2009 IRS publication 946 (How to depreciate property) billboards have a class life of 20 years and a recovery period of 15 years under MACRS and 20 years under ADS. Confirm this with a CPA.
Section 179 of the IRS tax code allows businesses to deduct the full purchase price of qualifying equipment purchased or financed during the tax year. (Federal not State) Qualifying equipment being tangible personal property. Real Property does not qualify for the Section 179 Deduction. Real Property is typically defined as Land, Buildings, Permanent Structures and the components of the Permanent Structures. Some other examples that would not qualify for the Section 179 Deduction include paved parking areas and fences. The key term is "permanent". If your billboard structure is considered "moveable" you could qualify for a 1 time depreciation deduction. Confirm this with a CPA.
Those with digital displays, those boards could have a shorter depreciation schedule than your structure. Once again, confirm this with a CPA.
Remember, tax planning takes place now, not in the weeks leading up to April 15th.