Testing Signs

One of the occupational hazards of a long daily commute is that your mind starts to wander into intellectual areas it really has no right to. For instance I've noticed recently that these traffic signs have got some new messages to display. Some are helpful and direct such as 'FASTEN YOUR SEATBELT' whereas some are somewhat more thought provoking....'COULD YOU TRUST YOUR SPARE'. All, you will notice, have questionable punctuation.

This particular one leaves a lot of unanswered questions for me and the more I think of it the more questions occur to me...

Who is testing the sign?

What's being tested...the signs ability to display a message or our ability to see it?

If it's truly being tested how do they know it works? Is there a camera somewhere to see what the sign says or do they send someone out to check?

Why this particular wording? Why not use some more informative text and see if that can be read?

OK, I'm going to have to stop this train of thought now...my head is hurting! Still I wonder what new message will await me on tomorrows sign ??