For this information will be of use to some. Certain information, markings, stamps etc on both letters and on envelopes white and brown, is traceable by those having such contacts. I can trace to an extent, or rather I can speculate, enough I think to be capable of doing a documentary if one would not get into trouble for it.
The post code etc can, and often is as in scam letters, an illegal address.
To be left with the occupier of the premises or, in his/her absence, left with a person in charge of the premises, or if no such person is present, left in a prominent place on the premises. This section of the pink paper, repeating in part but adding the end bit, is in an oblong upright box in the left corner, above the Copyright info. It was left on the plastic drawyer unit containing my coloring books a few feet inside the doorway. And the whole thing is now copyrighted to me.
Under the signature an MLX 31146
How about you David Cameron?