New business or not, it is a capital expenditure. Under an election, if the sign costs $2,500 or less you can write it off in the year it is placed in service so do not even have to jump through the Section 179 hurdles. If more than that amount, and you have enough business income, then you can use Section 179. If there is not sufficient business income and if the sign is new, then you can take 50% bonus depreciation then depreciate the rest as you normally would.