"As I went walkin',
I saw a sign there...
and the sign said,
But on the other side, it didn't say nothin'.
That side was made for you and me..."
-Woody Guthrie, This Land is Your Land
Using the backs of freeway signs is particularly effective on divided highways where exits are few and far between. I generally use hammer and nails along with binder clips and duct tape. Posting rarely takes longer than fifteen or twenty seconds and my actions are hidden, at least from those who could get to me, by the sign itself. Working at night brings your chances of getting caught to practically nil.