When pilots have to say letters or spell things on the radio, we use an international phonetic alphabet. You've heard it in movies: Alfa Bravo Charlie Delta Echo and so on. (If they are really old movies, you heard Able Baker Charlie, but that's another story.) The point is that we don't say "M as in Mike, W as in Whiskey ..." we just say "Mike Whiskey."
It's funny watching people who are not used to working with letters this way try to keep up with spelling. I can spell my name "Alfa Victor India Alfa Tango Romeo India X-ray" at a fairly leisurely pace, taking much more time than if I were just to say "A - V - I - A - T - R - I - X" but the non-pilot is desperately scrambling to figure it out fast enough to write it down. They can't decouple the initial letters from the meanings of the words. And when they have to come up with their own word equivalents they scramble amusingly to think of anything. I remember being given a password over the phone from a person who came up with "K as in ... Kindergarten!"
I had enough grocery store air miles (I must eat a lot) to fly to Yellowknife via Edmonton (I guess I'll hit Fort Smith another time) so I called an 888 number, listened to hold music for a bit, and got free flights. The friendly booking agent read me my confirmation "numbers" (they were all long strings of only letters), "V as in Victor, Q as in Quebec, E as in Echo ..." I wrote down the first one tediously, and read it back rapidly, "Victor, Quebec, Echo ..." to show that I didn't need the "as in" part. But she started on the next one the same way.
"It's okay, you really don't need to say 'as in.' I understand it the fast way."
"I know. I'm required to do it this way. Company policy." Okay, I'm not going to mess with her SOPs. She continued, "U as in Unicorn ..."
"Excuse me, did you say Unicorn?"
"Yes." Wow. I understand the substitution of Sam for Sierra. (C-what?) but how is Unicorn clearer than Uniform? That's just a dose of surrealism.
Unicorn. I love it. I'm going to try that on ATC next time I fly an airplane with a U in the call sign.