People sometimes use greek alphabet letters like "Alfa" "Beta" "Delta" "Omega". If you like those that's fine. But I think it should just be a fake name. Something not so obviously "Spy talk" but something accually secret.
there are some coll names of robot and one of them is Conrado
Guys:SworddrawerAxemanKilljoyGirls:BitethemdogsSwordchichotdagger
Israelites
Sora
krakow
riley
Fernando
rimshotqq
Here is a website with some actual spy code names so you can get the idea - if you're going to write, you need to learn how to come up with your own words and names.
some cool stage names are king, boss, lil Jac, kc, Justino, Sophinut, lil Chubbs, lil ganstaz
Some names of cool lettering include fonts such as Webdings and Wingdings. These fonts are designed to produce corresponding symbols when typing on a keyboard.
Heavenforth Mannar