I am not an expert on this, so I'm only guessing...
Google search throws up http://forums.about.com/n/pfx/forum.aspx?tsn=2&nav=messages&webtag=ab-german2&tid=987. Did you see that?
My guess (which agrees with some of the suggestions at the linked discussion):
Work along road -- all cars must stop suppose (=if) you look-him (=see) red fellow mark.
I'm not very clear what "red fellow mark" means. Is it a red picture of a man? (Though this doesn't seem particularly likely as a stop sign?). Or maybe "pela = fellow" is just used to mean "thing", or almost meaninglessly?