FWIW, I found that word of mouth was the best advertising.
I placed an ad in the Yellow Pages (once), and tracked any & all calls...in one year I got four (yes, 4) calls from 'the book'. Three were waste of time estimates, one resulted in a small job (>$300).
One of the 'large' contractors around here has a full page phone book ad ($$$$$), and all his fleet vehicles wrapped, and shirt & tie crews, and a really big sign on his shop. He does Elec, Plumb & HVAC & gets top, top dollar for all jobs.
I cannot ever remember any ECs with a billboard!