In terms of getting a message out - putting words in front of eyeballs - signs placed along the sides of freeways work best. The sign above, for example, replaces a similar one that stayed up for about three weeks next to the Hollywood Freeway. It was passed by over 110,000 cars per day, though I doubt it was seen by more than 35,000 people a day.
For those of you worried about such things, using the fencing and trees alongside the freeways is generally less stressful than overpass posting: more like putting up gentle reminders than in-your-face protests. Just about all urban freeways are surrounded by fencing, giving the discriminating freewayblogger hundreds of miles of potential posting spots.
Remember, all it takes to turn a fence into a billboard is cardboard, paint and a couple of bungee cords. Wearing a highway safety vest makes a person putting up a sign look like a person taking one down.
Signs placed high up tend to last a long time.
Signs placed at eye-level will last long too, provided they're hidden from pedestrian traffic and difficult to get to from the freeway. Most of these signs are only a couple of yards from traffic, but would take a couple of miles of driving to reach physically.
YTD - 437