I stayed at Elssie Tanners scribbled on a dirty tailboard. 
I can recall some Scroat in Slough chalked on the back cross member of my D1000 flat " Barbara Castle has one Harold Wilson is one" circa 1969 IIRC.
every trailer heading south in april-may 1978 would generally have someone writing “bulk scots for argentina " scrawled across the back doors.
around the same time,i did see a transit full of psycopathic mobile distilleries clad in tartan with argentina or bust heading down past beattock,then several hours later passing them at charnock with " bust” on the back doors as they waited lying up all over the embankment drinking their carry outs. 
‘Chuck of Little Lever’ on every transport cafe lavatory wall.
John.
How about the classic “CLEAN ME” with a ■■■■ and balls.
Pure genius.
AndieHyde:
How about the classic “CLEAN ME” with a ■■■■ and balls.Pure genius.
Or the more creative “I wish my Missus was this dirty” usually followed at some point by a cleaner (newer) “Oh she is mate trust me”
And the dirty white Transit with “Also available in white” on the back.
But a bygone one that was on vans, trucks, walls in fact anything and everything at one time was “Kilroy woz ere” with the doodle…
SID IS INNOCENT.
I still can’t believe that this was on Top Of The Pops in 1980. 
Free George Davis…with every four gallons.
On the back of trailers:
Fitted with air brakes. Kindly smile as you go under.
“Indian driver,smoke signals only” was another.
I remember when railways were on strike,Ray Buckton was the leader early 80s.It was all about flexible rostering.
A Goldenlay Egg artic passed me on night trunk on the A1 with “Goldenlay eggs,delivered fresh to your door,thanks to flexible roostering”.
And of course the timeless “Mummy mummy is Daddy dead? No duck,he’s waiting to load at Stanlow” or wherever. 
One I remember scrawled in grime on the rear doors of a trailer was:
‘A dog is for life, a turkey’s just for Christmas’
Robert
Then there was Passing side with arrow to right and Suicide to the left!
Don’t wash me,plant something!!
David
One that made me chuckle once upon a time:
If it’s urgent send it IPEC
If it’s indestructible sent it Dents
5thwheel:
Don’t wash me,plant something!!David
A variation was “Don’t wash, potatoes planted”.
Airbag test zone.
On a motor that passed me one day, signed "Say Dulux to your decorator " some wag had altered it to "Say Bolux to your decorator "
When the water shortage was on, Save water have a bath together and Come clean.
We had " Have Gravel Will Travel" On the back of one of our Tippers; Regards Larry.
Jeremy Thorp tells fibs!
did anyone else have a tigers.tail.from.esso??