Hi Alex, most certainly a strange one and as you say now that you know about it it can be seen on a variety of vehicles. Style and location vary but always on the same rear corner! Inspection mark? maybe, but why 'K' and what does it mean?
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Re my Ford, certainly appreciate some pictures when you sort them out. I have just repainted part of the front wing and trunk lid
ready for the change of vehicle marking,s now that I know its true original ones.
Ian