When editing the title to this question here on our sister site ELL:
my childish inner self was tempted to try and make some sort of scatological pun on the "p" in the question. Now, if you play enough scrabble, you may be aware of the notional spellings for the names of the English letters. The name of the letter P, for example, is spelled pee according to many dictionaries. This of course would enable one to come up with the pun in the title of this question—which I was tempted to use for that other question (for about five seconds).
However, on discussing this point with a colleague of mine, we both noted that we have never seen the word pee used in any piece of authentic written text. My colleague then ventured so far as to argue that he doubted that the written word pee even existed in any meaningful sense.
A search on Etymology Online reveals no results at all for a word pee referring to the letter. In addition, a search on Googlebooks for "How many pees in" yields no results. A search for "double pee" yeilds only one relevant result. However in that text, many of the other letters are spelled in ways not listed in any dictionary I have been able to reference - for example the letter I is spelled eye.
Even a search on Googlebooks for "the letter pee" only yielded five bona fide results, out of of which four results are in books printed since 2006 and one is from 1987.
My question therefore is what is the provenance for the spelling pee as used to represent the letter P? Has this spelling ever been used frequently enough for us to properly regard this as a standard spelling and what is the earliest known usage of this spelling of the word. Lastly, are there any alternative spellings of this word which have been in competition with this one?