@ is no part of the alphabet.
But it signifies "at," and "at" is arguably a word, as well as a common pair of letters found in other words. So, by his logic, @ should be considered a letter.
In my profession, # typically indicates "pound" rather than "number," And telephone voice mail systems tell you to press the pound key, not the number key. So # can stand in for pound, thus giving us words such as:
ex#
#ed
pro#
com#
con#
So, if y'all see me typing "Go # s&" I'm sure you'll know what I mean.