Impossible 3-dimensional lettering

[AndiFlatland]

Does anybody know what is the name of the lettering which is apparently 3-dimensional, but which is physically impossible?
To see what I mean (if you don't), go to a record site such as Amazon, and look at the sleeves for the Van der Graaf Generator albums World Record, Present, Godbluff or The Box (click on 'see larger image' under the picture to see greater detail).
You will see that the lettering has been cleverly drawn to look 3-dimensional, but closer inspection reveals that they can never exist as physical things, as the planes and angles are all wrong. In fact, they can be constructed, but they are only viewable as the letters from a single viewpoint - move away from it, and the illusion vanishes, leaving you with an object which looks nothing like what you first saw.
Does anybody know what this lettering is called, and who invented it? Was it Escher?

[kettledrum]

The artist you are thinking of is almost certainly M.C.Escher. I know about his 'impossible triangle', but I can't find any impossible letters / fonts.

[AndiFlatland]

OK, thanks, kettledrum!
I figured it probably was Escher, but all my searches via Google have proved inconclusive.
If you want to see the letters, I think just about the whole alphabet apart from Q and J is covered by the Van der Graaf Generator album titles - so have a look at them on Amazon if you want. The artist who did the sleeves must have worked out the lot when the idea was first mooted.