Thanks Lowlander (nor sure if you are classified as highlander or not
), but it feels kind of stupid to refer you to obdl3945...)
Since I have the book you refer to (and browsed through it yesterday, found nothing in particular) can you say where this is mentioned?
Anyway it is nice to get dates to these markings. I had in the back of my mind they came to around late 1939 and lasted roughly to spring 1940, which shows one should not rely on that place if it can be avoided...
Cheers
Stig