Did anyone see the ones on the m27 today heading towards Portsmouth telling with the words " Dont hog the middle lane" written on them. It made me chuckle while making a point too and i did notice some people actually move over to the left just after the passed it.
that notice was used last year also…
they seem to use it on bank holidays and weekends more on the m6 from what ive seen.
I wonder how many people check their fuel gauge after the sign which reads Check your fuel… 
lol no idea but ever notice how they are never close to a services
best ones are in sth wales with the time on them,as for the rest,
illuminated joke signs, i mean
queue caution? = some time in next 20 miles
que after next junction= 3 junctions later still looking for end of que
accident between M1 and M74 = no change there then(made up but you get the jist of it i .e M6 screwed up)
seen on M6 other day FELIXSTOWE closed due to high winds =
chavs in ipswich have got the hair dryers out again?
M6 toll clear? ,well it would be no bugger uses it 
bit like route advice from sat nav use with caution.
the ones on m25 are best 40mph i have a job get over 15 mph[/b]
OK I will try to answer some of these. 
“Don’t hog the middle lane”
As you said some did take notice. These are general messages from your happy to help HA. 
You will also see “don’t drink and drive” arround Christmas, and as said “Check your fuel” though I take the point about there proximity to motorway services. 
“Queue ahead” is usually set by an automatic system called MIDAS which detects slow or standing traffic and will show warnings at the last (or more in some areas where gantries are close) warning sign. Don’t forget there will always be a time lapse between the cause of the queue being cleared and the signals being cleared.
Accident at or Felixstowe closed is trying to give advanced warning so you can tell your traffic office in case that have something more useful to do.
As for 40 max, again this is MIDAS. It can only go as low as 40 but I know it seems to be taking the urine. 
There was a joke on the M40 ones that were installed a year or so ago during the afternoon one day. Just can’t remember what it said but looked like someone had found the control computer and typed it in for a laugh.
Like the ones on the M42 southbound on Weds…40…Congestion Stay In Lane and a ruddy great red X over the Hard Shoulder all the way from M6 4A to 3A for the M40, 3 lanes Solid and Slow moving…No Incidents, No Breakdowns on the Hard Shoulder and No-one Parked up in the Emergency Refuges…So much for ACTIVE TRAFFIC MANAGEMENT 