on the road...

[George A. Gleason]

...and in Berkeley the PD has a little trailer they set up all by itself,
which has a radar system in it and a display in large red numerals.  There
is a place to hang some large printed numbers representing the speed limit.
There is a large sign on the back which says, "Speed limit (printed
numbers); your speed: (red display numbers), drive safely!"  No tickets
dispensed, but pretty effective at getting people to slow down.