What does this say? Phrase hanging in Senator Barry Goldwater's office

GogLais

Ad Honorem
Sep 2013
5,490
Wirral
I went to a Uni whose motto was/is Veritate, Scientia, Labore. Usually translated as “Truly science is a bore”.
 

Linschoten

Ad Honoris
Aug 2010
16,217
Welsh Marches
It's cod Latin, a joke. 'Legitimus' is a proper Latin word, but 'illegitimus', plainly intended to mean 'bastard' here, is not (the Latin word is 'nothus'). 'Carborundum' is a word inverted as a trade name for the respective abrasive material, suggestiive of corundum set in carbon; but because of the 'undum' ending it looks like a gerundive verb ending, carrying the sense of should or ought to, 'carborundum' can thus be interpreted in context as belonging to the non-existent verb 'carborare', which would obviously mean grind or grind down. 'Noli permittere', if that is the right transcription, is more like proper Latin: so all in all, 'Don't let the bastards grind you down!'. I have heard it as 'illegtimis non carborundum', which is actually rather funnier.